as said by LL the reason ppl go for the 16v box is the mounts are already there, the mk4 box etc need a different bell housing.
regarding the 2nd gear crunching etc, this is a common problem with the 8v boxes as they are pretty weak, but the 16v boxes dont suffer from this
and regarding the oe management being hard to wire, meh i'll cross that bridge when I come to it
how hard can it be its just a load of wires!
there are a few quides that cover it if you search around, think its only 4 or 5 wires you need to splice together, most of the work is removing crap you dont need
Im done with this topic now, thinking about my engine just reminds me how poor i am