I was able to find a casting number on the gearbox 270280. It is listed in the Chevy parts manual as a gear assy. for a 1-1/2 ton. It has a p/n of 270927. Searching on the net, buyautoparts.com lists a 270280 as a gear box for a 3/4 ton. I will call them on Monday to see what more they can tell me. This does look like my gearbox and column.

http://shop.buyautoparts.com/search?view=grid&w=270280