Reply to OldNuc:
Wide Track. Special Parts. WSP The special parts are internal items relating to gearing usually and not bolt on items like PTO etc.
On D4 Specail parts can mean lots of diff external parts (wide topseat,sideseat,tailseat,side exaust,OD green paint,long trackframes,type of fenders,grill gaurd,type of seat, hood air intake, type of track pads, ECT) many things. In that era of D4 had ony one trans group. The bill of sale for my 2T5916 says Specail Parts installed were US War Dept. paint group(ODgreen green paint&seats) & tailseat group(All parts for tailseat arrangment)