Still working on the basket case. Serial 62M424 , per Nige commercial equivalent 66D5140 Has the old style injection pump casting number 5S7999. FPR casting number 7L7435 and the casting number of the elbow that goes between the pump body and the FPR is 2N7612. The gasket between those last two part numbers is what I am looking for. It has 5 oddly spaced bolt holes and two large sort of squarish main holes. The Cat shop was not much help. Said they will get back to me, you know how that goes.
Found one for sale on ebay for demonstration purposes. The gasket goes between the upper and lower half of this part.
#21 on the attachment seems to fit the bill.
That's the one, thanks. Got it ordered. Will be a relief when it comes because this thing has been dripping diesel since it blew.