I would think that, as long as the fuel system, the intake system, and the exhaust system were kept optimal (oh yeah, also the ignition system on them g@$$er thingies ), as long as the compression was good, you wouldn't lose any power.

But, those things have to stay happy...keep restrictions out of the intake system, keep the fuel system clean (clean/replace injectors, etc), and make sure that the muffler isn't getting clogged up (probably not a problem on a g@$$er, but you can get soot clogging a muffler up on a diesel). Other than changing spark plugs and wires, I don't know how to maintain an ignition system...to me, the only electrical parts are glow plugs and the alternator.

Just my $.02...it is also my belief that, if the compression's happy, an engine can be made to run as it's supposed to. This is in repsonse to some idiot who tried to tell me once that my '65 straight-6 would never again run like new, even though it had less than 60K miles on it...