Great ideas and TV rigs here!
The wife and I both like the older GWs, maybe one day we will get crazy and build one up. Either a GW or old Suburban 67-72 style... Either of course would be repowered with either a GM 6.5TD or 4BT.
My advice, drop the 4L60E and go for the beefier (and I think more driveable) 4L80E... Granted a NV4500 would be the gravy if you do not mind shifting!
+1 for a diesel repower as well. Although LS engines are cheap and plentiful, the gas mileage is sad. As is any gasser IMO on towing.
... I have an old J2000 sitting around for a "one of these days" project as well.