Offer them $500. When you need it, pull the dist and pour a quart down that hole (this takes a while). Tope off the oil (actually change it) Pull the plugss, put a tablespoon of ATF down there. Spin the starter a few reviolutions. Next day put the plus in, and the distribustor. Fire it up and enjoy it.
Don't over complicate it, just enjoy it.
If as advertised, this engine is certainly worth the $1500 asking price. Offering $500 is an insult.