My old Haynes manual does not have that listed, but if memory serves me correctly, it is 6 degrees BTDC. You can at least start there and go up until your get the dreaded ping. Don't forget that the firing older is the old school version of 1-5-4-2-6-3-7-8.
use total time. Run it up to about 3000rpm and set timing to28 degrees to start out then 32-34 degrees. then go back and check initial time. Could all be in the dist. coming in too soon.
8 degrees before top dead center
attach timing lead to #1 cyl
disconnect vaccum advance from distributor, plug hose with thumb,
set to 8 - 10btdc
reattach vac hose raise rpm to 2500-3000 and see how many degrees it says
( should be around 30)
and dont buy cheap gas