Tearing it down

If it's a 318 (which it probably is since it's a roller block and 302 heads were used on 318 roller engines) the J heads will lower the compression due to their open chambers vs. the closed chamber's on the 302 heads. 302 heads are good heads for a small cube engine so if it's a teen they'll work fine. The cam you have isn't real big yet I don't think it'll help low end torque. It might even loose some low end but it will open it up a good amount in the mid to upper range. You could still use your cam and overcome it with a high stall converter. You basically have a few way's to go. Keep the short block you have and use the cam kit you have along with a higher stall converter. Or install a mild roller cam in it. This will be very easy to do and fairly cheap cause you can find a set of stock roller lifters and the spider retainer and you can get a stock roller cam re-ground. Plan it right with the heads you have and it'll run good. You do need to get shed of the exhaust rotators and put better springs on it and check to make sure the lift doesn't cause interference with the retainers/valve guides. If you want to upgrade the heads look into a set of RHS or Engine Quest heads. You can buy them in the small valve version really cheap. If you find it is a 318 and want more you can look for a 360 to replace it with. The cam you have will do nicely in a mild 360.