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Maybe I missed something but what's wrong with your engine?
I like it!Just hunt around for remanufactured engines... as an example Jasper Engines is one place but I've never used them. Either that or see if GM has a crate replacement engine for it.
Other than high mileage, what overall condition is the rest of the car? It sounds like it has been a good investment.
Maybe stick a 350 in it?