I've seen pics of guys that have had problems with air cleaner interference. "Where there's a will, there's a way." Maybe build and air box? I put a Holley 470TA on my 225 cid Buick V6. I think a 470 would probably work well on the 258 and 304 as well. Even though it is way too much carb for both 6cyl engines, with a lot of tuning I feel that the 4v performs head and shoulders above my old Rochester 2G. It is not "out of the box performance" like the literture advertises because you're not bolting it onto the engine that the literature advertises, so don't expect to be perfectly satisfied the same afternoon you install; it will take you a few sessions of evaluating your driving habits under different jets, power valves and springs to get it dialed down to your cid.
One of the nicest performance improvements I've noticed is a remarkable gain in fuel economy. Because you can tune the primaries and secondaries independently, I have gone from a miserable 11mpg using the Rochester to an almost unbelieveable, yet fairly consistent, 17-19mpg. That's running 4.88 gears and 33" MT tires! The reliability, instant throttle response, ability to tune the primary and secondary independently, and off camber performance have been well worth it, IMHO.