If you're afraid the age of the plane will affect the motor mounts, then the plane probably shouldn't be flown to begin with. The motor mount screws should go into blind nuts on the bottom of the beams. If they don't, if they're wood screws instead of bolts they should be replaced. Or if even one is stripped out, first chore will be to repair or replace those beams. They're Maple btw. In a proper build those beams would have been fuel proofed with a coat of epoxy, dope or some kind of fuel proof paint. I prefer epoxy myself but dope soaks into the wood better. If the beams appear to be raw wood, they are most likely fuel soaked and should be replaced. Not easy but not impossible either. Power tools can be your friend here!

To properly inspect the motor mount beams, you'll need to remove the engine anyway. And putting it in a test stand prevents the possibility of fuselage damage and/or a runaway (where the fuselage gets away from whom ever or what ever is holding it! Always happens at full throttle btw.) A test stand also gives you full access to the motor for any adjustments.

Download the plans I posted earlier. You're local Staples should be able to print them out for you at full size. They will help you. Especially if you need to make any new parts.

And as for old airplanes, I have a Proctor Mini-Antic that is pushing 40 years old. Still flies regularly. Weekly when the weather and schedule cooperates. Still a solid model and never a broken glue joint. They can be built to last!