I sent Sean Carlini my axles last summer to measure. You guys were going to build me a set to test in my race car but after several months I had to get my old axles back. Sean said he would send me a set when available and I would still like to try the RCV axles if you produce them.
For a 351 I doubt you need more than a 650 carb. My 331 in the prerunner with GT40 heads, 9.5:1 and Comp 270HR cam uses a 600 and runs great. The Ford 351 crate motors for circle track racing recommend a specific 650, you might look into one of those. Better yet, call Cliff or John at C&J Engineerin...