Mike,
My 418W stroker has been using as much
oil also. I replaced the intake gasket last year and that resolved a lot of my smoking during the downhill high vacuum (read copious amounts). However, I still use a quart every 250-300 miles. Rings have been excluded and the culprit is in the valve seals and/or guides. I have Edelbrock Victor Jr heads that have been using this
oil since new. Car has 9800 miles on it now.
Several weeks ago I drilled and tapped my intake mainfold for a dedicated vacuum port for the brakes. As I was cleaning out the manifold runner as carefully as possible to remove any residual aluminum shavings down in the runner, I slipped my shop vac hose, with a 3/8" adapted clear hose, slowly down the runner. As it got close to the valve, it sucked up a small amount of
oil! This is not mormal! Bottom line is that I will need to pull the heads and have them rebuilt with new seals and guides. May as well CNC port 'em while they're out. The motor itself runs great. strong and does not blow blue smoke out the exhaust during acceleration, but does puff a little while going downhill for a period of time. Good luck with your fix and I hope this helped.