ol' slant is dead... need help!

$1800 sounds fair for a rebuild long block w/ warranty, but

You should be able to get a good, used slant six almost free, since people here can't even sell them when they upgrade to a V-8. Worst-case is a $250 junkyard engine. You can turn one over by hand and feel for each cylinder to insure it is good. I recall a lot of rebuilt ones in wooden crates from a government warehouse sold on ebay a few years for ~$500 each (hydraulic cam type).