700R4 to NP205 Question?

[72longbed]

I know this has been discussed on here a lot, but I can't seem to find the answer to this question: I need to know what output shaft length to use when adapting my 2WD 700R4 to my NP205? I'll be using an NP205 that was mated to a TH350 tranny, and it still has the TH350 adapter bolted to it. I'll also be using the 'spacer/adapter' from 'Red's somebody'?, that goes between the tranny and the TH350 adapter. I'm not going to use the Advance Adapters shaft, I'm using a stock GM shaft and need to know which one to use.
Do I buy the GM 13 1/4" output shaft or something else?? Oh yea, how many splines do I need on the output shaft to work with that 'Red's spacer??

Thanks a lot,
72longbed