Need info on slant six engine

Check the Holley PN. A small 4-bbl (370 cfm) is ideal. If so, don't lose it since those are rare and cost more than a common larger one. In theory, it could even give better mileage than a 1 or 2 bbl. I sure wouldn't say "over-carb'ed" without knowing the PN and also what camshaft is in it. The 4-spd manual tranny is also rare and very desired. But, I am guessing the seller knew all this, unless it was something like an estate sale by relatives who did not appreciate the car.