I wouldn't run Rotella in a modern engine, the tolerances are way too tight these days. But for a early 1960's Chrysler big block, particularly one with some miles on it, 15W-40 will work just fine.
I think when the 413 and the 727 were pulled from the wrecked Imperial that had 64,000 miles on them. The 727 got a rebuild, the engine was used as is. When I do a hot restart there is a fair amount of smoke comes out of the breathable oil fill cap. But overall consumption is low and has actually gotten better now that I cured the over heating issue with a proper fan.
We drive this little spine compressor a couple thousand mile a Summer max. Fun to take out as cars like this are uncommon in our area and it draws attention wherever we go. The interior is, shall we say, compact? A runt like me fits pretty good. There were a couple of 6 ft. plus potential buyers before I got a chance to make an offer on it, but they simply could not drive it. Also requires left foot braking, which I have done my entire driving life.
I always got bitched at by State Patrol instructors at EVOC school, but when there was actual timed "competitions" the only guy that could beat my course times were, me. Instructors from the local Tech Criminal Justice programs were a bit less anal. Wanna have some fun? Put an instructor riding shotgun, a female reporter from the local TV station and her camera man in the rear seat. The Instructor just left me alone to do all the backing maneuvers with mirrors, palm the wheel, and flat out go! Clapped out Crown Vic with a good motor and fresh tranny, but steel belts showing through the rear tires and all the room needed for the course in an NFL stadium parking lot gated off for a few days. There you wanna talk about under steer?