You can make an EFI 304 go pretty hard too by stroking it to 350 or 377ci, and sometimes this is easier and cheaper if you already have a decent driveline like a TH400 and 9", brand new heavy duty radiator etc. But nowadays it is becoming just s easy to but an LS1 or LS2 in as you can stick the auto in as well and if you have to buy all new conversion bits like radiator etc it makes sense.