You should use a t/stat as an engine running to cold is problematic .....sure you may have heard of others doing it ......but its there for a reason .
No reason why you couldnt fit your own p hose as you describe , Id just drill a hole and put a nipple in it ( like a brass nipple not......
) . Just gotta remember that this hose will only tell you the water has got as far as the hose , not that the cooling system is fully flooded.
Probly the 1st thing to do is find /figure out how the water flows thru the motor and follow the flow untill you find the restriction . It maybe that you have to remove the ex plate or the head to get at all the passages . Does the thermostat housing look all crudded up......might be a good indication of the rest of the cooling system.
The removal of the head and ex plate involves the removal of corroded bolts and that in itself is a whole nother skill.
I read here somewhere that someone tipped a couple of gallons of vinegar into a tub of water and ran the motor in that ......which aparently got rid of the scale in his motor .........sounds feasible
.
This doesnt have to be a hard problem to solve, probly your biggest pita will be removing seized bolts etc .
