Unless you want the rather considerable expense of thorough non-destructive testing ~ ~ ~ such as dye-penetrant and Magna-Flux, maybe even X-ray &/or ultra-sound ~ ~ ~ unless you really think you need any or all of those procedures, there is a rationale to re-building a used case. Old-timers refer to them as being "seasoned", which I guess is similar to 'seasoning' a new cast iron skillet.
If you are comfortable with the absolute knowledge of the source of your used case and know that the engine it came from was actually running OK the last time it was shut down, clean it up - immaculately! Then, visually examine it as closely as you know how. Ask for help: there is nothing like a second set of eyeballs that may see something you missed. Get out your best sets of micrometers, bore-gauges and calipers and mike the bloody thing; again, as closely as you know how. Heck, even if you are going to trust a new case to keeping your rear-end in the air you'll probably do all of the same inspection work, any way . . . . . . . . I have yet to fly a Vee-dub, but have rebuilt several of Dr. Porche's beauties for automotive use. Never once started with a new case. Even hopping-up a couple of them for off-road racing and dune-bugging in The Imperial Valley/Yuma desert areas, where/when we ran the hell out of them in the very worst of environments, we NEVER had a failure of an accepted & inspected used case! Well, that's not exactly true. We did have one failure in a used case that we had cleaned up, inspected and found acceptable. We sent it out for machine shop work - boring & stroking, etc. Even installed needle-bearing mains on the crank. Damned thing was a real work of art. Unfortunately,we did NOT re-check the machine shop's work as closely as we should have . . . . . . . Three cylinder/head hold-down bolts on one of the cylinders pulled out of the case. Nutz! s/s WxBY - ORL/MCO (_jtwxby@AOL.com_ (mailto:jtw...@aol.com) )