wow, that's in awesome condition! great find.
the C code black block should be in there, lemme know if you need anything for the motor or the transmission. it should have a TH400 in the 2500 frame, but I don't think it is a true 2500, it's a 5 lug, van. so it could have a 200R or 700R or a th350 even. look at the block and see if it's red.

as a pricing comparison... a full set of 8 pistons cost me 52.00 (I have a spare set if ya needs one...) 5 pistons for a MB 617turbo cost... 1600.00