NIce post Gordy, apparently those instrumentals with Peter Tosh were never meant to be released, apparently on some or most of them he was just playing along to the track without being serious. You're right, most of them are rubbish - except for the version of "Uncle Joe" on the B side of "Moon Hop", entitled "Harris Wheel" - thats brilliant.
I also agree with you about the UK stuff, most of it is tenth rate apart from Dandy's productions on Downtown, the early ones.