I wouldn't bother to tune a 305. All the tuning you can do on a 305 will just get you to where a 350 is stock. If you want more power, you can score a 350 and ECM from Pull-A-Part for dirt cheap. It's just labor on your part.
I have just the opposite thought. If the 305 is solid, bolt parts on it that can transfer to a 350 later on. The 305 is only ~20 hp down. Headers, free flowing muffler, Volant air intake, better cooling, etc. If it is an automatic I like the S10 converter. The 305 would enjoy a cam around 212 @ 0.050 on the intake side and that could transfer into a 350. The PCM tune is not all that expensive and once the PCM is jail broken so to speak the tuner can segment swap over the 350 engine tuning if it is ever needed. The L30 305 I had in the Tahoe made far more power than a stock L31 did.
