A few thoughts:

Will twin turbos raise the price enough to pay for them? Will they require high octane fuel?

If the car has tubs and big tires, a big-inch smallblock might sell. Just do something with the top of the motor to suggest big power....a scoop....multicarbs...etc. Late model injection would give it an interesting look, too.

With the gas scare, and the result I am seeing in parts of the hobby already, I'd bet on the hot smallblock! Driveability, cost of the build, broader appeal,etc.