Deisel will probably last the longest and have the best torque, but diesel fuel is also much more expensive than regular gasoline is. And I don't think that the economy of the diesel is enough to offset the higher fuel price. There is no "best"---BUT the LS 1(and up) motors are some of the best built, highest horsepower per buck that you'll ever find. There's a truck dismantler near me and he sells 4.8's and 5.3's to a whole bunch of people for hot rods and conversions. I bought a 90K mile example from him last year for my '51. For $1400.00 I got a 4.8 with a 4l60E the wiring harness AND that harness reworked, reprogrammed, VATS removed and computer reflashed. I can't rebuild a 216 for that kind of money, not that i would. 300 HP, 300ft/lbs of torque, 20 mpg. You just can't get that amount of all around performance for that little money anywhere else. There are 4 wires to connect and that's it. If you keep the AC compressor on there, you can add an AC unit later on. Power steering pump is already there. You do need to change your steering column, but if you go to power steering, that would need to be redone anyway. I'm keeping the stock wheel and column but going with a 70's power steering box.
Don't get me wrong, I like my inlines just as much as the next guy, but for that kind of money, I couldn't put a rebuilt 6 cyl. in there for less money than the LS motor, trans and fuel injection.
