No. 44 rear mounted hydraulic pump

That is quite interesting. I have only seen some 41's on D2 and D4 tractors. That would be unique. Most around here use Be-Ge units. JM

Apparently they were used on D4s d6s d7s and d8s according to my parts book.

You might want to consider mounting on the front. That way you have live hydraulics rather than having to shift to neutral if you want to raise your blade if you are stopped. I would think that it would be easier to find parts for the front mount rather than the rare rear mount. Just my 2 cents worth. Grant.

The rear mounting hardware and drive pieces is going to be a real needle in a very very big hay stack to find. I can only think of one such on a 7u D4. The family that had it where IH people and traded it for a TD 6 at the first chance they had, so long gone from my neighborhood. Several friends and I would make 3 or 4 trips a year to large used parts yards. Spending the day looking for the odd and miscellanies parts and don't ever remember any rear mounted Cat pumps. Of course the Cat dealer owned yard never allowed us the freedom wonder the grounds like the other places. But also heard they don't leave slow moving parts sit for year ether.

So if you are really set on having a Cat unit on the rear, hopefully you have someone that is a talented machinist to make some of or all the mounting and drive hardware.