Everything you think may be true but just to play devil's advocate....the guy you got the engine from may not have known about any problems with the engine. A slight variation in compression is hard to notice unless you do a compression test. As for the block ears, you didn't notice them yourself when you bought it so it's unlikely the previous owner knew they were bad. As for blaming E-bay, I think that is totally unfair. If you were ripped off in any way, it was the seller, not E-bay. It would be no different than answering a newpaper ad, you wouldn't blame the newspaper would you? Sorry about your situation but those are the chances you take, and in this case, they should be fixable without breaking the bank. A '74 engine of any mileage needs to be freshened. You really expected 37+ year old valve seals to be in good shape?