I'm doing it now with a lockup trans in my 74 D100 and it's been done a number of times before by guys here. Nothing new. PATC transmissions has the instructions. The pressure switch comes from chevy 250 & 350 transmissions and cost about $5 at the trans supply. It's the thrid gear clutch switch. I think the part # is A44416AA. The letters at the end are the code for the pressure. That # comes in everything from 55 to 40psi depending on the last letter or letters.Drive shaft will need to be 3.5" shorter also. If you aren't using a lock up then you just need a toggle switch for on and off and a pressure switch for in and out of OD.