How do you tell what liter your Slant 6 is?

water pumps are sure cheaper for classics than for modern cars.
Same for alternators, starters, etc. I have gotten many parts real cheap on ebay, like $25 for a new Carter BBD carburetor. You just have to spend time and search PN's. There are a few rare parts that could disable you, so stock-pile. For a slant, the exhaust manifold is one. Good thing is you can get a used engine/tranny almost free from the many people changing to a V-8. Ditto for the rear end. You just need a place to store them.