Engines of 50s era had larger tolerances. For that reason alone, I'd use 20w50 or at least a 10w30 or a 30 or 40w HD. Checking the oil at every fillup was a good practice in those days
Funny I just re-maned a 67 buick 340-4 block and the crank pins checked out at 0.0022 > .0.0023 which is a one-thousandth running clearance. I did clean up some pins on a ford 351 and that had a wide tolerance of almost a thou instead of a 1/2 thou or less.
That's about the best you can do given block distortion and crank harmonics.
I think I've seen some honda's running under a thou, I have never measured the bearing width or dia on those.
I might guess they need to be a tad wider and possibly fatter to work with the 20 grade low HTHS oil
Piston tech has moved a bit with the silicon hypereutectec and plasma moly short skirts but I'm hearing more noise with them.
Oh and I forgot , we tore into this "low mileage" engine to check out an odd noise.
It had two wiped cam lobes. Car had under 70K on it.
That's with high ZDDP oil and over the nose of under 160 lbs!
So after its broken in I'd go for the moly.
Race cam you should have roller followers. But.
"Motorcycle" and ATV 4T oil has HIgh ZDDP and is a light 40 grade.
its usually API S- rated in to the (now obsolete) high zinc period of pre SL