Freeze plugs starting to go...273 V8

Hello Gang,

I have a question for the group. As most of the members here know, I have an old '68 Plymouth Valiant with a 273 V8. A few months ago, I had the car in the shop to diagnose another antifreeze leak. I had the radiator replaced recently and the radiator itself is fine. The mechanic had said that the 'freeze plugs' are starting to go in the engine block. How hard are these plugs to replace and where can I obtain the replacement plugs? I'm hoping that this is not the end of the engine or the car...The mechanic had said that some of the plugs are easy to get to, but apparently the trans has to be dropped to reach one of the plugs on the back of the engine. It sounds like a costly operation...

Could something be poured in to seal the plugs (like Stop leak, that is used for radiator leaks?) Any information would be greatly appreciated.

Sincerely yours,

Brian T. Carotenuto