RBT,
like your motto ,... gas vs. diesel,... same here. there's a couple things you will run into,... the 60's & 70's models are considerably shorter on the front frams, from the firewall to the front crossbar. the 80's & up units, like 1BG,... are longer, thus more room to work with. the next issue is that the allison's.... AT540,542,545,..etc. are much longer than the manual tranny's . so that complicates the working room for the ''intermediate'' shaft , especially removing it for service.
the 4BT fits much nicer in the older units, and the weight ratio cuts it down to 200 lbs. , instead of 500 lbs.
plenty of power, fuel economy ,..well there's no comparison, and doesn't beat the machine to death. well some people can, no matter what.
ive tried to shove all kinds of engines into these things,.. these comments arte just the tip of the iceberg,.. but i say,... DIESEL it up