Nothing will line up perfectly but a newer model will come close. I think that a Suburban NT-24
is what would be the closest replacement.
I have replaced the furnace twice, once in a '72 Overlander and also in the '73 Sovereign
that I have now. I did have to build a small frame for it to sit on (it ducts down in front) and had to move it just slightly to the right (aft 3/4" from original mount position) to make the exhaust/intake line up).
Here are some pics
of my furnace and I have others as well. (I am starting to forget exactly how I did it though, so hopefully the pics will be self-explanatory.) There's also a good thread
on it and I posted some pics along with some other members.