Dualie,
You and I are neighbors .... I live near the San Leandro / San Lorenzo / Hayward border areas.
For what ever it is worth prior to my joining this board in 2003 , for the 30 years I had been driving I used nothing but straight 30 WT HD oils in all my cars ... From a 1962 Dodge 3/4 Ton ,Datsun 510, 68 Camaro 327 , 69 El Camino 327 / 427 , 79 Old's 305 Chevy , 77 Monte Carlo 350 , 70 Ply GTX , ect ect ect....... No flatheads other than an old lawn mower....
My old next door neighbor used to have a 34 Ford PU with a flathead V8 and he using straight 30wt also.....
But in our climate where it only gets to 30 deg F a couple times a year and only at night and rarely goes over 105 deg F ..... I NEVER had any issues with a straight weight HD oil...... Some here will have you belive that a straight weight oil couldn't possibly work...... but I did it for 30 plus years.
Now I use only multivis in my newer cars for and whats left of my stash of oil SJ Delo 15W-40 in my solid flat tappet 427 Chevy.
I just go down to Vic Hubbard's and get my oil and filters.... well pretty much all my car parts from Vic Hubbard's........ they have been around since 1948 or so....But I did see several cases of DELO 30 wt the last time I was in their warehouse behind the store front.