Looks like a rebuilt engine does indeed require special care to ensure a long life. Checking the oil frequently, having the oil changed at specific points, and a bunch of advice about avoiding constant RPMs and possibly about avoiding "long trips". I don't know if the "long trip" advice is more about the tendency on a long trip to have your engine RPMs stay at the same (lowish) levels for long periods of time, or about running your engine hot rather than cold; I'd suggest asking your mechanic.

I expect that instructions for such a big older-technology engine may differ some from the advice for current engines, but having googled for ["rebuilt engine" "break in" -motorcycle], here are some of the links: engines, motorcycle engines, and some random yahoos going on about engine break-in.

Regarding long trips, I take some encouragement from a comment made by some random yahoo in that last link, about how he did well "driving this way across Kansas for the first 500 miles - no normal driving, just repeated acceleration and coasting". (You should read the link for details...)