Is 20W-50 too heavy for my 340?

I buy LOTS of diesel oil when it's on sale (oil change in both my diesels, bye-bye 24 quarts)
I was given a couple cases of old racing oil, loaded with zinc. Trouble is, it's straight 50 wt.
So, in my flat tappet solid lifter 440, I use a mix of 10-40 diesel, and a couple quarts of 50 wt (out of eight)
I'm sure somebody will say it's a terrible mistake...... but it works for me.
(I save the thin watery synthetic for my late model muscle car that requires it).
Imo, bottom line? Run the 20/50.