TH350-NP203 to TH700R4-NP208

[1985K10]

My 77 GMC has a TH350-NP203 setup, but I was considering swapping to a TH700R4-NP208 setup. I have a 700R4-208 truck(1984), I know id have to use the 208 crossmember and drill the frame, but what about the trans tunnel, could I bolt in the "cover" from the NP208 truck? And are the u-joints(driveshaft to diff) the same??

I would like to use the 77 axles, and is the shifter the same? I know the marker thing would need to be changed(P R N L1 L2 vs. P R OD D 2 1)

Im sure someone has done this!!!

Thanks!