gear vendor/dana dilemna

[gordo1968charger]

i started fitting my gear vendor over christmas,disaster struck in that the coupler that goes from there tailshaft adapter to the actual overdrive was too big,the splines did nt fit.
i thought the conversion was going too well.
year one are in the process of rectifying this.
however before i started this after fitting my strange dana,i was going to put the driveshaft back on and see what difference it made,but the yolk(is this the right term) would nt fit to the new part of the dana,is it possible to swap this from my old 8.75?
my plan C is possibly order a custom drive shaft from strange to the right length with the right ends on.
what do you guys think?
thanks in advance
gordo