Dual 19.5 wheels are common on a P-30, and so are the 5/10 lug....
However in earlier years GM made some single wheel step vans and other vehicles that ended up with 19.5" 8 lug single wheels.
They are a little hard to find now, but well worth finding if you can. Using an 8R19.5 tire keeps the original tall and skinny look of a 1 ton, about 32-33" tall. I have some on my truck and like them a lot.
