If soda blasting is not available you can heat the undercoating with a heat gun and scrape most of it away then wirebrush the rest after you scraped everything.
In my opinion an automatic transmission with a full manual valve body is the most fun. You get the benefit of a torque converter but still get to choose the gear.
Tear everything apart and use a lot of marked bags for the parts. Get everything media blasted. Do the necessary welding. Get the welds sand blasted again. Put primer on. Put the body filler on. Put the paint on. Put the clear on. Assemble everything again.