RE: Wild (possibly heretical) notion
They are iron and steel. The porting is good enough for diesel but not very good for glow. The extra heat generated by glow fuel doesn't have a direct path to travel and in my opinion that is a problem. It would be possible to do, but I don't think it would work out that well.
For those that are not familiar with diesels built as diesels they typically have an extra long cylinder liner at the top, well past the top of the piston. This is to allow the contra piston to be fitted and seal well, no o-rings needed. In the case of the PAW 55 and 80 the outside of the cylinder is threaded and the cooling fin "head" unit screws onto the cylinder. A glow head to replace the contra would have to be made of steel.