That is a huge engine bay and would look strange with most of the smaller engines unless all bulked up with turbos and such stuff.
My 460 is already built and installed, but if I had to do it over today I would still go 460 - but with CJ aluminum heads and intake to bring the weight down. Even more brute torque and horsepower for a reasonable price, without having to deal with complexities/costs of turbo's, electronic controls, etc.
CJ aluminum heads and intake are not cheap either, but core 460's abundant and available cheap. When built up modestly, you get all the power you could want (or most people would want) in a fairly simple and easier to repair and troubleshoot package than the newer engines - and it all pretty much bolts together.
Plus, there is an abundance of bolt on parts to be had aftermarket since some of these cars came with 429 and the 460 is the same motor with a longer stroke.
Even with the big block I have a reasonable amount of room to work around motor, though if using headers that would make it a little tougher. My car just uses 429 PI exhaust manifolds which flow better than stock 460 manifolds and fit well. Extra horses from headers weren't worth the headaches of adding them to me.
I agree with previous poster that said the weight is the biggest downside of the 429/460, but if you can afford the cost of turbos and extensive mod's or acquisition costs for some of the newer/smaller motors, the aluminum heads for 429/460 are probably cheaper in the long run than all the mod's - and you don't end up with a car that is too far removed in appearance or complexity from what the factory issued.
Also agree that both 351c and 351w are even easier, no big weight penalty and can get by without aluminum heads, if that cost is a factor. Plus they have the most flexibility as far as your choice of transmissions. Not sure why anyone would use a 302 (or stroked to 347 302), being it is a tiny motor and engine bay is too big visually for it.
I have built a couple 460's, 351C, have a 351W on test run stand and building an aluminum head 302 right now. But the 302 is going in an MGB, so it doesn't look like a peanut in the MGB engine bay, while it would in my 73. No one of these all Ford motors has been noticeably more costly to rebuild than others yet either.
In fact, the both my DOVE headed 460's were cheaper to build than the 302 (and would have been even without the aluminum heads on 302), but that is mostly a function of inflation apparently, as 460's were built years ago and 302 just now.
Machine shop prices for boring, head rebuilding, etc. are a lot higher than 15-20 years ago. But having a block machined or heads rebuilt isn't much different from one engine family or displacement to another these days.
So, I'd go with 429/460 first (the most torque for the money), then either 351C or 351W (both can be stroked to about 400 CI without breaking the bank too, if displacement is an issue and you dislike the 429/460 option). Again mostly everything bolts together.. But why stroke a smaller motor to get more displacement when BB is probably even cheaper with even more displacement and will be more durable as well, since it is not stretched to its limits?
Coyotes, LS motors, 302 or V6? All fine motors for other applications, but in a 71-73 engine bay? Why torture yourself and your finances when both simpler and cheaper options are available that fit the car appropriately?
Regardless of how fond you are of the car, some day you will tire of the car and want or need to sell it. The odder the combination, the worse beating you will take on parting with it. Nobody else has one equipped that way? That's cuz almost nobody really wants them modified that way and that will become apparent when you try to sell it, if it isn't now.
My two cents...
