Posting this on behalf of a coworker's husband. Here is the info he sent me.
He is looking for alternatives to the 2year OCI of M1 15W50; each OC is >$50 I suggested an OTC diesel once a year (before I knew the mfg rec weight was 20W-50) This seems to be the type of engine I would be wary of using oil with reduced anti-wear. Anybody have any out of the box ideas on this one? I suppose sticking with his regimen isn't out of the question.
I have been using Mobil1 15 w 50. The original spec for oil in the Alfa calls for 20 w 50, which I believe is due to the DOHC with buckets and shims. It was a pretty hi-performance engine for the time (1967) with an all aluminum block and head, removable steel cylinder liners (makes rebuilds easy), forged 5 bearing crank, hemi head with a center spark plug, twin cams with chain drive, and two twin barrel side draught Webers (all 4 barrels open all the time, no secondaries like a domestic 4 barrel). It also has a 5 speed and 4 wheel discs, kind of unusual in 67. On the other hand it’s only 1600cc’s (about 100 ci) and is rated at 125 SAE HP ( which I think gives higher ratings that the current and more accurate DIN system). It’s a high revving engine, with the red line at about 6700, but most people will rev the 1600 to around 7500 with no problems. I rebuilt the engine about 25k ago, total mileage is about 2k to 2.5k a year.