My '73 P-400 has a 300/4.9 with an NP435; this assembly has one (two-piece) mount at the very front of the engine, and two at the bellhousing. Did any IDI diesels come installed this way?

 

yup, when they were installed in international medium duty trucks.

 

Any idea if those mounts happen to line up with Ford's?

 

they should.
i think the big problem is going to be finding a set.

 

Those mounts are part of the SAE bellhousing adaptor. You will be forced to run a medium duty transmission. No need for these mounts, just do mounts off the frame to the idi.

 

I could make my own, sure, but I'm considering engine swap options and using the stock mounts would be an advantage. A medium-duty trans would be fine; this rig might qualify as a medium-duty truck.10k GVW, 2-ton payload, DRW.

 

So long as you have the space in the firewall and transmission tunnel, that SAE bell adapter takes up a heck of a lot of real estate.