Preferred Transmission question

i'm slowly rowing in that direction and my choice is purt much made up to go with a 500/42RH

currently running 727, but figured that the "smaller trans" offered a better advantage with lower gear set and less parasitic loss, weight and size.

i've resigned myself to the fact that i'm going to have to "custom build" the trans to my spec and that there will be some scavenging of parts from other things and stuffs, but ultimately it's the same amount of work, time & price to get installed between the two units-- unless somebody has proof positive otherwise, that is.

however if a 518/46 presented itself it's not like i'd kick it out of bed for eating crackers.