Just to update y'all.
Put her in the hands of a competent former head LR mechanic who owns several D-90s, series, and works on nothing but LR and literally within half an hour, the pump was off, packed with vaseline, put on and she started up. Sounded rough at first but smoothed out and purred like before within a couple of minutes. He says the amount of copper was minimal, and he's seen worse cases last longer, so he says I should get another 100k!!!!
Anyway, want to thank all of you guys for your advice, input, offers of engines both near and far, and helping me get the hell away from this Other guy who so clearly should not claim to be an experienced (&/or competent) LR mechanic.
1994 Silver DEFENDER 90 NAS SW