I got that much timing with two light springs bringing in the mechanical advance at idle. Cranked the base way up and ran the 30 degree vacuum can on manifold vacuum, . It didn't matter on a 260, around 4000 rpm was probably pinging some, sounded like life was coming to an end. He should be able to run close to 50 at idle and 60 part throttle with mechanical and manifold vacuum advance. I don't know if it is the flat valve angle, long runners or chamber design or all the above. Either way, the Olds V8 likes part throttle timing.
