While I have 78 M400 with a 440, I had no problem removing the mounting bolts. You do however have to remove all the front grill center section components. What bolt are you having trouble accessing?
The metal mounting shroud (part the bolts attach to) around the core, top tank, and bottom tank is all soldered together and comes out as a single unit. You only remove the bolts shown in the picture. The radiator rebuilder has to reattach the top tank, bottom tank and metal mounting shroud to the new core.
BTW - There was no "house" on the chassis when Dodge built it.
Link to someone who took a little different approach: http://www.mywinnebago.com/blog/inde...y090726-211323
. That is howerver a 413 not a 440. You can at least see what the old radiator does look like out of the chassis.