Exhaust would have nothing to do with oil consumption.
If you are running synthetic oil, the next change stop using it. First, you don't need it. Older engines just can't handle how slippery it is and it will leak past old seals and gaskets.
Take the top off the air filter and look at the vent hose from the valve cover where it enters. Is there oil showing?
I would try reducing the highway speeds to 55. '70-'75 is damn fast in a 720. This is less than 15 min each way extra and will reduce the oil fog inside the engine and the blow by that pushes it out.
Speaking of oil...
Look up discussions about how oil makers are reducing the levels of ZDDP a zinc anti scuff additive that is important to 'flat tappet' cams like we still have. All new cars use roller cams and it isn't needed so it's being fazed out. I'm running 15w40 Shell Rotella T4 a light duty diesel oil that still retains the higher level for diesel engines. Castrol, Valvoline and a couple of others still market what they call 'racing oils' that still have the original higher levels.
Not really the safety I was concerned with but the extra revs will produce more blow by. If it is excessive the fine oil fog in the crankcase has less time to settle out and can be pushed out and carried along the valve cover hose into the carb.
I drove my 710 last winter for the first time. Nothing like winter driving to show up problems. Carb icing for one. Installed the 'stove pipe' and all good. The hesitation when taking off got gad enough to backfire and blow up the muffler.... cracked coil arcing. Not a problem in the summer just annoying. Now it runs so much better. I'll never drive it in the winter again!
Castrol does make a racing oil with the higher ZDDP level and probably 10W30.