As mentioned by RAMCHARGR, I think it is easiest and best to re-use the in cab part you have and adapt it to the compressor on the 4B. The evaporator coil inside would need checked and is likely OK. With the appropriate expansion valve and freeze switch, it can be adapted to the compressor on the 4B... or a Sanden replacement.

Classic Auto Air in Florida can recondition the in cab part or DIY. Bouchillon is a great source as well.