John,
Here's a sketch of the jig I made for the hinge mortises. It only took about 20 minutes to make the jig and the new mortises came out as good or better than the old ones...and the best part was it didn't cost me anything
**You can use any cutter/guide bushing combination that produces a 1/8" offset with this jig. For example, I used a 3/4" bushing with a 1/2" cutter, but it would also work with a 1" bushing & 3/4"cutter, a 5/8" bushing & 3/8" cutter, a 1/2" bushing & 1/4" cutter and so on....
Greg