Castrol GTX 20-50

I currently use Lucas 10/40 hot rod and classic in a Chevy 307, a B-Body 383 and the 340 in the Duster. I did however recently change the oil and put VR1 20/50 in the 383 when I was diagnosing an engine noise, thinking it may be related to oil pressure(didn't wind up being related to this after all was said and done). Couldn't find Castrol 20/50 on the shelf locally. Great oil pressure to say the least with the VR1 20/50.