Transmission should not be a problem. Allisons auto's (old style AT545 or similar) or various manuals will bolt right up. Lots of old manual transmissions at local wrecking yards. I saw that aluminum block on ebay also. You might want to buy a "parts" 471 to get all the components you will need at a reasonable cost. Rebuild kits will have liners, pistons and that, but lots of small parts will be required, and buying them from a parts store could get expensive.
83 C10 Suburban, Silverado, 6.2, 700R4, 3.73, 31-10.50R15
82 C30 Crew Cab dually, 6.2, Banks, Th400, 4.10, Gear Vendors, 235-85R16
83 C20 Suburban, Sierra Classic, 6.2, 700R4, 4.10, custom paint, 285-50R20
95 Yukon, 6.5, 4L80E, 3.42, 265-50R20
73 GMC Astro 95, 8V71, 10 speed Roadranger, 110" WB, 6 each 11R24.5