He's already had a compression check done and the mechanic said one bad hole. Can it be much simpler?\
It's a two-barrel 273 which should run on the cheapest gas out there.
Replacing the valve is a possibility and would probably be good for 20,000 miles if the seat isn't damaged.
If the seat is damaged I'd go straight to the 'yard and pull a 318 out of a 1985 - 1988 Fifth Avenue. Dress it in the 273's externals so your belt drives and exhaust system don't cost money. You may need to use the 318s 2-barrel manifold with your stock carb because of bolt hole angle differences.
My 100K+ '86 318 had absolutely no ridge and the bearings were nearly untouched. It would have run for another 100K without any changes.
R.