Re: amc turbo400/gm 400????
It may depend on whether the GM400 is a 2WD or 4WD model. The actual bolt patterns should be the same 6 hole pattern so the D20 adapter would mount up fine to either GM 400. The potential problem area I think is the tailshaft.
I think the 2WD GM model with its tailshaft will bolt right up to the D20 adapter and D20 case. The reason I say this is I know my tranny guy used a standard 30 spline 2WD output shaft when he changed out the 10 splined q-trac tailshaft on my amc400. We compared the 2WD shaft to the shaft on my donor J series amc400 and they were the same spline count and length. The only difference was the 2WD shaft had a speedo gear on it, but it was not in a place that interfered with any thing on the D20 adapter or D20 case. I dont know if the GM 4WD shaft is the same length or not
Hope this helps.
77 CJ7, D44s, Detroits, 4:27s, 35 SSRs, HS9500i
84 CJ8, 33s, REP8000