Get a couple of 45 degree pipe elbows and a couple or 3 pipe nipples of the right length and you should be in business. That's what I did on my 656 a few years ago. I used 2 inch but since you said large, the 766 may take 2 1/2 inch pipe.
Here's the deal on brakes. The brakes shown on the MD are Lambert style disc brakes and could be had from the factory as shown in parts books. They are identified by having 3 bolts in the housing verses the IH style of disc brakes having 5 bolts in housing. Super M tractors all had the IH disc brakes as did the very last few thousand regular M's. As for the M&W pump, it will fit but the distributor cap will be mighty close to the oil filter. Just be sure the pump is for a diesel and not a gas tractor in order to have the correct rotation.
If anyone is wanting a factory 2 pth , 2 row IH corn planter, model C-251 I believe, I know where one is. PM me if interested with your phone number and I will call. Located in west Ky.