273 to 340 swap

And you can bore the 360 out to 4.04 and call it a 340 stroker, now it's being a 367. It can do Everything the 340 can do. If you build it to the same horsepower, it will get better fuel economy, maybe run on cheaper gas, and need less rear gear, to be a much more fun tractor of an engine/city-friendly combo.
But if you build it up with the same 340 type parts with lots of compression,that little 268/276/114 cam will pull like a diesel tractor, while reving to the moon, and getting thru the the traps quicker and faster than the 340.And she'll probably do it with 1 size smaller rear gear.
But if you bolt it together with 8.0 compression, it will still make more torque than the late 340s with also similar CR ratios.
There's just no losing with a 360, except perception. The 340s got the reputation, the 360s got the rap-utation. Taintso when they are similarly street-built.
But if you have your heart set on a 340, the 68 stick engines were the hottest, the 68 to 72s were the next hottest, and the 73-ups; well some call them slugs. While they 73-up CRs were down, this mostly affected their low-rpm operation. Just crank the timing back in and they were still pretty good performers.Make that; really good, for 73up
None of this is likely to mean much to you, cuz any old 340 you can find today is likely gonna need a rebuild, and then you can pick and choose to build what you want or need. Or perhaps you get lucky, and someone else has already done it for you.
But if a 340 is not written in stone, then a 360Magnum is probably the best thing going these days;or at least it could be with a little forethought.
Physically, they are all pretty much the same. Paint them red and it will take a keen eye to tell them apart.A stroker 318 is a special case. It looks exactly like a 318 on the outside; EXACTLY. Yet they have been bored out to 4.00 and stroked to 4.00, and that makes 402 cubes, or plus 26% displacement. And that is a game-changer. In your GT that's about 7 pounds per cubic inches. SEVEN!
My 68 Barracuda at 3450pounds would need 493 cubes to match that.
So at 402, you can pretty much build it as tame as you want and still be the bully on the block.
If you were to build it up to 1hp per cube, it would make 402 hp, and have the potential to drive your GT to over 120mph, perhaps mid 11s in street trim.
If you built it tame, about the tamest you could make would be .75 hp per cube or 300 hp. 300hp. That's already on par with an early 340, that was pushing .9hp per cube. Ok but; 300 could push your GT to around 110 in the qtr.Still really fast.And that tame engine could make an awesome streeter. Mega-smallblock-torque. You will not be able to put big enough tires into the stock tubs to tame the torque. Nor will the smallest gears tame it. Nor the smallest TC.
But if you went middle of the road, at say .88hp per cube, giving up some of that mega torque which overpowers the chassis, now you have the potential for 350 hp and 116mph in the qtr. It will still have too much torque for the chassis, but it will also have alotta pull on the top. A LOT!.
And it still looks like a 318 on the outside. In fact, you could even put the 2bbl back on, and not even know the difference until well past the speed-limit! Talk about being a giant killer.
Of course I suppose you could do this to a 360, for an extra 6 cubes...... The only easily visible difference would be the right-side engine lugs................yes the teener top-end will bolt right on,lol