Hypothetical build questions…

I've done this swap a time or two.
I have used the stock 340 short
with 318 heads, and I have used both
a stock 318 cam, or a stock 360 2bbl cam; installed straight up.
I used a Factory cast-iron dual-plane Small-port, spreadbore intake with a Thermoquad.
This makes your 340 basically, a big-bore 318, with a magnificent bottom- end. It will pull any gears. But
If you have the A833od then you can run a lot more starter gear than what you think might be right.

I suggest a cruising rpm of not less than 2200, (because that is already pushing the ability of the factory type distributor to provide adequate cruise-timing) and with a .73 overdrive, and 26.5" rear tires, that points to 3.73s; for 2200=64mph.
However, this makes the starter gear to be; 3.73 x 3.09=11.53 which is way more than this combo needs, but it will be a lotta fun. But more importantly;
Second gear will be 3.73 x 1.67=6.23 which is perfect.

Now, there is one caveat. The CCP with the Tall pistons in there,
may be much too high to use the 318 cam; too high probably for WOT detonation-free operation, no matter what gas is in it. So you are gonna have to carefully measure the Scr, and adjust it as may be required, to get the CCP into the required window with the Ica of whatever cam you stick in there, so as to make it streetable.
But, I would try to keep the CCP as high as is possible to run the cam of your choice.
There are two or three reasons for this;
1) when the bug bites for a bigger cam, you won't have to throw away as much CCP, which, with a manual-trans, you usually don't want to do.
2) Big CCP helps make Big Fuel-economy.
3) Big CCP will increase the Low-rpm Torque, so yo don't have to slip the clutch out so long, and you can still burn ribber whenever you want to......

You may ask;
1) Why the 318 small-port heads? Answer, with 3.73s and a 1.67 Second gear ratio, 65mph will be about 5100 rpm, and the 318 heads will easily be enough.
2) Why the 318 cam? Answer, cuz it's the right cam to go 5100 rpm with, for starters, but more importantly; the specs are;
240/248/112 @.008 But that is only half the story,
in at split overlap, the specs are;
240 intake/130 compression/122 power /248 exh/20*overlap.
With this information we can figure out a few things;
1) Because the overlap is so very small, this tells us that the Headers are overkill, but you already got them, they won't hurt anything, and the inertial-tuning will still work.
2) with 130* of compression, she is gonna make a lotta cylinder-pressure in those very modest sized chambers, with pop-up pistons.
3) Normally 122* of extraction is ridiculously large. But in this case, combined with the other specs, this is gonna extract about as much energy out of the expanding gasses as will ever be possible. This means "massive" low-rpm torque, for an SBM, which makes for the possibility of extracting modern-day 4-banger type Fuel-Economy.
4) So since the CCP with the 318 cam is gonna be so huge, I have found the 360 cam to be acceptable. The new specs, in straight up, are;
252intake/123 compression/119 power/256 exh/30* overlap.
This does several things for us; notably;
The pressure will be down about 12 psi or more, helping shed some of that excess pressure. Power extraction is only 3* less, but really, it was excessive with the 318 cam anyway.
This 360 cam is almost 2 sizes bigger than the 318 cam, so the power-peak is gonna go up some 300 rpm. This wont't make much of a power increase with the 318 heads, but it will extend the operating range, at least the same 300 rpm, which will get you 70 mph@5500 in Second gear; so that's a good trade.
5) the overlap is now 30 degrees, so not a lot but I bet the headers will find it.
6) the hardest part of this marriage, IMO, is gonna be setting up the timing curves. You will need to mod every moving part in the distributor, and yur gonna need a lotta Vacuum advance, and
I highly recommend you find a dash-mounted, adjustable, timing module. or an electronically programmable distributor.

The first time I did this was in about 1975. The engine went into a 1965 V100 station wagon, with an A904. It didn't corner very well, but in a straight line, it was "btchng. Oh and, she was my DD for 2 years, and made fantastic fuel economy. I still have that engine/trans, as I sold the car without it. To this day, I still have fond memories of it; and wish I still had it, cuz with what I have learned since then, I think she would corner a lot better today.
This post, is of course, a reflection of what I might do, and in no way is it a "you-just-gotta-do-it my way, lol.

This combo with a 360 top-end, and cam that has more than 44* of overlap, will be just as much fun, but will never achieve the mpgs of either of the factory 2bbl cams. The cost of gas will never go down again, but will steadily march upwards until it becomes unafford for most of us, so I have to look ahead to buying the cheapest gas out there and have to make it work. To that end, I would target CCP of 155psi or perhaps a little less.