Any 1987 or newer 350 chevy engine would be a good candidate to replace the 305. All 87 and newer 350's have roller cams and good flow characteristics. Tune port injected motors have good strong mid range and stock will rev to 5500rpm's. Another motor to consider is the 1991 and newer LT1 or LS1 350's, although you will need a donor car or after market wiring looms to complete this conversion. The best transmission for this swap will be the 700 R4, but it has to be beefed up to take anything more than 250 horse. Have fun. =)