Should I replace the engine in my 1991 Acura?

150000 miles 1991 Acura Legend v.6 engine

The car has had excellent maintenance before we owned it. It has had heating problems for the past year. We had a new radiator put in, new starter, new battery, new radiator hose that blew. It has smelled like antifreeze. We also had the A/C fixed which works well now. The body and interior are in great shape. The head gasket jsut blew and we don't knwo why it over-heated. Word is here it will cost $2000 for a new gasket and we still won't know if the engine is cracked until we fix the gasket. One mechanic said they wouldn't even put the head gasket on because it bites them when the engine still doesn't work well. I am thinkign about putting in a used engine for $3500. I live in Savnnah, Georgia and the used car market here is pretty bad. I don't think I can get a car this nice looking and with it's history of great maintenance.
the only question is; what about a down-payment on a new car, like a hybrid instead of this risk on a used engine? What do you advise? Many Thanks!