I was able to check a couple of places in town today. From what I saw, straight SAE 90 is still safe. All multi-viscosity oils I found today were either GL-5 or GL-4/GL-5. AutoZone had Pennzoil Synchromesh, which is GL-3, for $8.99 per quart. Our local farm store had Champion SAE 90 GL-3 for $27.99 per 2-1/2 gallon jug. NAPA was closed by the time I got there. At least I have options locally.

-Tim
'51 Chevy 3104 w/'56 235, 848 Head, HEI Dizzy, Corvette Cam, Split Manifold and Dual Carter YF's