you have your Truck all set up for a 350, just take the 307 out and put a 350 in. the 350 has a lot more power stock than a 307 and it would take a lot of machining to get the 307 up in power, you could boost it a little with a set of headders and a cam and new intake but, a stock 350 would cost less than all that and you would end up with more power, just get the oldest 350 you can, the comp raito's were higher, pre '71 especially.