I would not run anything below 15/50 on a street car in the summer. 5/30 is ok for a motor with tight bearing clearances or a 1/4 car that gets cooled after every short blast.

Just for giggles have you check the rocker shaft install. bin done before and I did it back in the days before time and had extremely low idle pressure and it was a rocker shaft with rocker oiling holes up!!! disregard with roller rockers