I would recommend Valvoline 10W40 for older high mileage engines as it has all of the detergents that a street driven motor needs and about two thirds of the zinc you need to keep the cam alive. Depending upon your spring pressure you might need more, but I doubt it with a hydraulic cam. I went with a 40 weight as it needs a little more oil pressure when cold to keep the oil moving around the motor.
Keep in mind the cam is splash lubricated just like with your lawn mower engine. Until you get it warmed up be gentle, once warmed up you need to keep the RPM's up to lube the cam.
There are reams of information written on ZDDP on line and if you wish to wade through it you will learn a lot about oil. The BBC is really hard on valve train and requires as much help as you can give it, which is why I switched over to roller cams back in the late sixties.