Which Transmission to use?

A 518 has 727 front guts. A 727 is comparable to a C6 and th400. A 700 uses th350 low reverse clutches and planetaries. A 2004R is weaker than a 700. The A500 has the same overdrive as the 518, but of course weaker clutches; comparable to a 2004R, but it has a nice low first gear. Both A500 and A518 require floor surgery above the mount area; but it can be performed from above; for the most part. I hate using GM because then you are required to use SPECIAL parts like flexplate and starter. Good luck finding replacements when the time comes. Under 400 horse I say go with the A500, but use Kevlar front band and thin Red Eagle clutches. 5 in forward and 6 in direct. A radical 340 should use the A518; add a clutch to the direct 3 pack.