Kyle- I'm doing a 3.4 V6 build as well. The reasoning is this - I want a car suitable for reasonably fast touring, decent stoplight performance, one that will be fun on a twisty road, provide creature comforts like A/C and probably power windows and steering.
One of the criteria was that the car had to be capable of 30+mpg on unleaded REGULAR ( 87 octane ). By utilizing the torque of the 3.4 vs. the horsepower of a more exotic engine, all of my criteria can be met. And as a bonus, the 3.4 weighs about the same as the B-16. n With the fuel injection, altitude changes create no issues.

At the moment, unleaded regular goes for upwards of 30 cents per gallon CHEAPER than 91-92 octane.

The other engine I have considered ( but not measured ) is the Rover/Buick aluminum V8, which was used in production up to 2004. I know it is narrower than the 3.4 across the pulleys, so might fit better between the frame rails of the PV444-544. While it is entirely possible to get good performance out of the various 4 bangers, that will almost always require the use of premium fuel.