Maybe the head can be saved by chasing the threads when the plugs come out or with threaded inserts. Seems you’re in over your head (ha!) at this point so pull the head and take it to a reputable machine shop.

606 heads aren’t easy to find separate from the block or car. Check car-part.com

Curious about the km odometer. Is it a Canadian or Mexican car or an SDS modification?

Sixto
98 E320s sedan and wagon