My first comment was that for a DD an 80 is nice except for the gas mileage but since you owned one, you already know that.
And since you owned an 80 you know that general maintenance is not cheap in general...Yes they will run forever (almost) but an older rig like this will surely need more in the way of maintenance.
For a $500 difference in price I personally would let someone else deal with the engine swap...
I guess my general thought is things never seem to go as planned and if by the time you are done you are into this rig for $7500 will it still look to be that good of a deal? I don't know...I have a super short commute so for me the crappy gas mileage in an 80 is bearable. Otherwise I'd be looking for a DD that got in the mid 20+ mpgs