SM 420 ? transfer case ? ls1 ?

[67GMC3/4]

I am trying to get a plan of attack together for my 67 GMC 3/4 4x4, it seems to have a 327 small block, sm420 4 speed, dana 60 rear, dana 44 front but any idea on what the transfer case would be ? so I have a few ?s about these two,
currently the truck has 32 inch tires and everything else appears stock but at 50 - 55 mph it seems to be maxing out at speed, any ideas what the stock gear ratio options were ? I am planning on swapping to a c5 corvette ls1, dana 60 front, and 37 inch tires, would a freshened up and cryo treated sm420 take the abuse of an ls1 ? or a supercharged ls1 ? also any suggestions on what transfer case combination and gear ratios to run if I plan on mudding and trail driving the truck with trips to the sand dunes as well ? want something that will allow me to go down the highway at a decent rpm level and still pull me out of trouble. I was also considering swapping to a jeep 5 speed trans and transfer case any suggestions appreciated, thanks



thanks guys.