The 436 just has a little shorter swing, in combines side by side the 466 will eat the 436 for lunch but I'm not really sure if you need the output of the 466 or not. I'd be curious the difference in torque ratings at similar horsepower.
Both the 436 and 466 are rather efficient engines, both my 1460 and 80's will generally burn 3 quarts to a gallon an acre.
The 1480 with the 436 was kind of an odd duck first place (far less interchangeable parts to the newer combines) so it should be alot cheaper. I doubt there is any difference in the pump so similar power should be achieved but you might have higher exhaust temps under heavy load. With the cooling system not running in the dirt a combine has to deal with it may not be a problem at all. A turbo swap to something like an HX40 would probably solve that if it was an issue.
I believe all the AMBAC pumps had an 11 mm plunger but would be something to look into, the MW inline was only 10mm if I remember the numbers correctly, I welcome someone to correct me if I am wrong.
I believe at full rack travel on the MW I am capped at around 325-330 hp in theory but the 706 with 303 at the PTO proves there might be just a little more life in there than goes to theory.
I got one apart laying outside right now at 6000 hrs and still has very nice cross hatch in it but three of the liners are scored due to a bad water pump from A&I, 2nd bad experience with one of thier water pumps loosing the seal in under an hour of use. Stay away from that junk, they didn't even have enough decency to replace the last water pump, the first one the dealer ate and replaced with Case IH.
For a bit of extra cooling capacity get a water pump pully and belts for a 1680 with the 466