I’m starting to restore my 1975 Chevy Caprice Classic convertible. It’s been sitting in my fathers garage since 1994/95. I started out by pulling the radiator to replace because it was completely dry and rusted through out and when I pulled the thermostat housing, there was no thermostat but a lot of rust and crap.( see pictures) The lower radiator hose had rusted debris in it and the inside of the water pump where it was attached was corroded. When I try and turn the crankshaft pulley with a socket, it doesn’t move. So before I bother to continue pulling the intake and heads should I assume that the engine is seized and dead? Would it make sense to try and have it completely rebuilt( it’s a 400 small block) or should I just drop in a new full dressed crate engine?

Thermostat should be here

Water pump

thermostat should be here

 

I'd drop some kind of motor in there. The corrosion and internal damage is too bad for a rebuild, IMO.

 

No telling what the bores look like but sounds like a history
of poor maintenance.

Depending on how your "modern motor" skills are, might suggest
something like pulling a 6.0L LQ9/4L80E with harness out of a
2500HD pickup wreck. I just went through a 700R4 swap that
still isn't right, and shoulda sold the mildly built 400 instead since
I have the tuning tools for many GM vehicles.