Re: Going lsx in a 72 El Camino
Wow... thought I got a great deal on my 5.3 @ 300. Between the 5.3 or 6.0, the 6.0 will probably net the same MPG you're already getting. All Chevy auto transmission will bolt right up, so if you want to keep your 200-4R, you might only need to modify the flex plate.
But, I'm surprised at your MPG #s. Before I tore mine apart, I was getting 17-18 highway and that's with the TH350, but 2.73 rear gearing. I would likely have done better had I known some of the issues I've since discovered after tearing it apart (like the HEI being run off the resistance wire, stretched timing chain making making timing adjustments almost pointless, vacuum leaks, etc).
That 5.3 was originally intended for my El Camino, but I've since rethought that and decided to stay with the SBC. I will eventually go with an OD trans and change out the rear gearing for something like 3.42 or 3.73. I'm dumping the carb and got an Edelbrock EFI kit.
1972 El Camino Custom
2005 SSR 6-speed