[Kurt in NJ]

The front, center caps are Steel in all years, the rear cap is Steel early, cast later, the steel caps are tinned, the iron rear cap is done the same as the block, and has to be peined---
The picture is what you would get back in the day at the dealership when the krw system was used, new factory caps, you can see the indentations from the factory peining which were large washers pounded in with air hammer

I had a lot of trouble getting a good bond trying to pour caps, many failures---- but like Herm said, using a torch won't give the temperature control that is needed