[1crosscut]

Don't be overly quick on pulling the radiator out or to treat with vinegar.
First read up on how to properly set your timing and get that correct. Many, many over heating problems are caused by timing not being set properly.
Myself I am not a fan of the vinegar treatment. To me it seems that it has the potential to break a lot of rust free causing it to migrate into your radiator making matters worse. (just my opinion)
If setting the timing doesn't help with the over heating and you do pull the radiator try cleaning it with undiluted Simple Green. Plug the lower outlet and the over flow tube and put in 1 gallon of the Simple Green. Put the radiator cap back on and invert the radiator several times. Walk away and let it soak for a while. Do this several times a day for a few days before dumping it out. I think you could be quite surprised on just how much crud comes out. Often there is a lot of grease inside a radiator from overzealous use of a grease gun on the water pump.

Chris in CT has suggested a good way to look for looseness in the steering assembly by having your Grandfather move the wheel back and forth. The only thing I would do differently would be to leave the front wheels on the ground while doing it.

If you still have the loss of power and back fire issues after fixing the intake manifold leak take a look at the flexible wire under the movable plate in the distributor. The wire could be bad and and or shorting out. Also check to be sure your points are set correctly. If the have closed up it can cause some of your symptoms.

It might be a good idea to re-check the torque on your head. Having it spew coolant out when going up hills make me think that you could be pushing combustion gases into the cooling system under the added load of going up hill.

Aren't these old cars fun!!!