I'm assuming you know about the design flaw in the 3.5 liter version of your engine, if not do a search and settle in for some reading.

If your car has a replacement shorblock engine installed in 93 I don't think you have the new version of the connecting rods that solved the issue with this engine.

A new shortblock, with the updated rods, should fix your problems forever. I'm not sure I'd be willing to drop 6-7K on a car that only worth maybe 7-8K but if you really like it and want to drive it long enough to recoup the investment a new engine would be a reasonable investment.