I agree that the motor could be coming up on it's last leg, but if we take the guys experience and living situation into account, then we should start him out with the simple/cheap/free fixes and then go from there.
Slant sixes are tough engines and you can still make a dying engine run well enough to get you around town without being too annoying. Maybe for a few dollars we can scrape another couple years out of this engine with some better mileage? By that time he could possibly have built up his experience and have a new place so he can go buy a new motor and install it himself.
