If they ripped off the cooler lines and ran the tranny "dry" till it wouldn't move,I'd say its toast...on a TH350,reverse is usually the gear that you lose first when the tranny is dying....you may luck out,but I wouldn't get your hopes up,if it moves in the forward gears but no reverse,its likely one of the piston seals or the clutches for reverse are smoked...............................................................................................................................................................................................................................................................................................................the TH350 I had in my 77 GMC started shifting into reverse "slowly" when it was getting ready to croak,then one day after I'd let it sit a long time it refused to back up,all I heard was a slight "stripping" buzzing type noise.........I found if I left it IN reverse for up to 10 minutes,it would finally "semi-engauge" enough to back the truck out of the parking spot...only did that twice,then it refused to do anything in reverse at all...weird thing was all forward gears worked fine,it was just reverse that "dissapeared"...that was the final straw for that truck,I parted it instead of fixing it,due to rusty frame issues and other discouragement..I assumed all the abuse and thousands of shifts from forward to reverse using it to plow,just took a toll on reverse the most?...