What do you think the best power/drivability combo is?

I agree with Bobzilla. If the cost of building your own turbocharged ride isn’t to scary for your wallet, it is a home run IMO.

The great thing about a turbo is how easy it is on engine parts. In a over simplified way.
The engine is basically running down the Hwy. on zero boost and doing what it would do as a NA engine. So a small engine, like a 273, 318, can get 20-ish mpg and then get a boost from the turbo for power when you he demand comes in from you.

As always, a big roll in mileage and power come from the camshaft. Finding a cam that can deliver booth is the trick. Unless, there is no care in mileage. At 5/6 hundred ponies, I don’t think you car. LMAO!!!!

As I said earlier, it will take a lot less cam to do that power level. Bigger engine, smaller cam, moderate boost levels.

Are you pondering a turbo build and if so, at what displacement?

Gas mileage will depend on your foot and how often you.get into boost lol. You can get some great mileage, just depends on the size turbo. Low boost numbers usually help mileage like under 10 but still giving you good power too. Open distance I would go with air to air. Thinking twin or just a single?

Just kind of toying with the idea at the time, but I have other things I want to do first.
I need to get my 8.25 locker with disc brakes and maybe a triple pass 2-one inch core tubes radiator first, and then I'll need something else to do.:D
Very likely add AC as well.

If I end up doing it, it will be with my 5.9 and very likely throttle body injection.
Right now the cam is 214/224 with .512 lift and 110 LSA with the Hughes 1110 spring kit.
I would probably go with something like the self learning EFI, but not sure what brand.
I already have 3/8 EFI line all the way up and back and I can build an in tank pump setup.