looks like a dual MOSFET with the body layer connected externally. also looks like a 1970's piece of equipment. the FET has probably been out of production for 30 years. you can probably look up DUAL MOSFET or DIFFERENTIAL MOSFET, but these days you won't find anything with the body layer connection, and i don't think it will affect anything, as the circuit it's connected to is just to make sure the body layer has the proper bias relationship to the rest of the device, something that modern MOSFETs take care of internally.