340 4 speed vs 5.2 5 speed

Why not just slide the 340 short under all the 5.9 junk.
You could probably take one cam size outta that performance combo, as compared to the 5.2, and still make more average power than the 5.2 with it's one size bigger cam.
That would also let you run one rear gear smaller, and help in the fuel-mileage dept. That's a double win.
EDIT: Ok that made sense when I wrote it,lol. What I mean is this; You could run a 340 with a 210 cam, to match a 5.2 with a 218 cam, and the 340 car could run 3.23s compared to the 5.2 with 3.55s; AND, both cars might have similar WOT performance, while the 340 car might post 8 or 10% better fuel economy;there, now it makes sense.

You, OP, have to understand that x amount of horsepower, on two different cubic inch engines, produces two different power curves.
On the street,
with two same vehicles, the one with more average power over the rpm range you are limited to, is gonna pound the other.
If both engine were built to 300hp, with no tricky porting work, and by the combo, both are set up the same; then the
Smaller one is gonna need more rpm to make the same 300, which means a bigger cam. The later closing intake of the bigger cam, is gonna reduce the cylinder pressure, which is gonna reduce the low rpm power. So; the
bigger one is gonna blast off harder and be quicker to redline...... cuz it has more power down low.
But say you fixed the pressure problem. Now, the smaller is less lazy on the bottom, but it can NEVER match the larger because the smaller has a cam designed to operate at a higher rpm.
So therefore, again, the smaller gets left behind.
But say, you also re-geared the smaller so that it matched the take-off torque of the larger, and now they both take off the same. You still have two problems;
1) you are gonna run out of revs sooner, and have to shift, and then the bigger is gonna blast by you, and
2) your bigger cammed engine is still gonna have a weaker midrange, and it could well be that the bigger will still make more average power, before you have to shift, again leaving you in the dust.

Ok, on the street, average power and TM (TorqueMultiplication) are king.
The only way you are gonna match or surpass the bigger engine, is if your gears are gonna multiply your smaller power, to a higher level than the larger.
And guess what; if you are both running the same trans, then the only option is more rear gear. And if it requires a lot of rear gear, then tirespin becomes an issue. And, at the other end you get into a higher reving cruise rpm, with it's attendant lower fuel economy, exacerbated by the bigger cam.
So whenever Performance WITH Fuel Economy is important, it always points to lower cruise rpm, and an earlier closing intake valve...... and that points to a bigger engine. And if that bigger engine happens to have a longer stroke....... guess what, you can put a slightly bigger cam in it, before losing cylinder pressure. This can be used to advantage, by reducing the low-rpm power and easing the tirespin problem.
On the street, it's not always about absolute power. It is about having the right amount of power at the right time, and for the most amount of time.
To this end, the 5-speed manual trans is the right starting point .......... as long as the engine doesn't blow it up.
And finally, You can diss the 340 all you want, that doesn't change the facts;
It's still nearly 7% bigger,
It has a bigger bore to fit bigger valves into
It came with a higher compression ratio, which will always produce more cylinder pressure, with all other parameters being equal.
The heads have bigger ports and bigger valves. Which, on the street may not be a big deal, but nevertheless the potential is there.
That factory 5.2 intake is very heavily biased for torque production..... which limits it's power production. When you put a regular 4bbl on the 5.2, you are gonna have a whole nuther opinion of the 5.2. The 340 already has probably the finest cast-iron intake ever factory installed, and the TQ spreadbore set-up, on the street is hard to beat.
That 5.2 cam is also heavily biased towards torque production. That's why as a stocker, the 5.2 seems very powerful...... Then couple that with gearing, and you get the impression that the 5.2 is a powerhouse. Remember earlier I said that on the street,it's not always about absolute power? Here is your prime example of that.
The 340 was heavily biased towards power production but was handicapped with two things; log-manifolds and lazy gearing; the two exact things that a racer would immediately change. For many guys,Nothing else needed to be changed. This took a 14.5second car waay down into the 13s, just these two changes.
So just because you read about the factory 340 only having 275 gross/240 net-hp, doesn't mean the factory 230 Net 5.2 is gonna be anywhere near the 340car, going thru the traps.

Install new lightweight pistons into the 340, get it balanced, and then, Slide her under the 5.2 junk, with a proper modest cam.... and headers ............ the follow it up with the right rear gear and make a two-gear street monster, that still get decent mileage.
No!
No, I'm not hating the teener. You can get just about whatever performance level you want,on the street, with a well thought out 5.2Combo. You just can't cover all the bases with it, as well as you can with a bigger engine.
And it doesn't have to be a stroker either, with it's preponderance of low-rpm torque, that you are gonna either have to figure out how to harness .... or live with it.
At 10 cubes per pound,(3400pounds car and driver) the 340 just naturally falls into a nice performance slot. For a 5.2 to fall into the same slot, the vehicle would need to be 3180 car and driver. Then, badaboom! Line 'em up and see what happens.