So I went for it this weekend and replaced the blend door and the heater core on the 97 E350. Had no heat. A few estimates to get it fix for around $1600.
Took me about 2 days of going to the parts store, waiting for parts and trying to get some of the damn screws out. The one at the top of the heater core box is an SOB for sure. Other problem were the heater hose quick connects (not sure I would call them quick). Actually took me longer to get it apart than to put it back together.
All said and done, I now have heat.

A few scratches, curse words and maybe a tool or two dropped really hard.
For some reason the rear ac has no heat but for now. I dont sit in the back.