I've got an old can of STP from the 60's sitting proudly on a display shelf in my shop. Theres one of those stainless steel punch-funnels laying beside it. They are a constant reminder of the good ole days to me. I punched many a can of oil & STP into all kinds of engines when I was a gas jockey back in the day grin Mine are for display only tho....

There are several modern oils availble that contain ZDDP at close to old time amounts and there are also ZDDP additives availble to add to your regular oil. I'd go one of those routes for ZDDP.
Dave

1949 Chevy 1/2-Ton 3100
1949 GMC 1/2-ton 100
In the Stovebolt Gallery
More pix on Photobucket
Video of the 216 running
Video of a Winter Cruise