Mike,
Thanks for the good response!
If you were going the usual "slap a 350/454 with a TH350" in it, then I would say "don't destroy that great old truck you heathen!"
But a Detroit/Allison combo.... hmmmmm.... a few of us have remarked in the past that it would be cool if someone did something like that (I'm partial to Cummins, myself). Actually, your idea is starting to sound pretty cool. You have my blessing, then (for whatever THAT's worth...)
Be sure to take lots of pictures as you go along, and keep a journal, so we can make a feature project out of it for the Tech Tips section!
Regards,
John