These IH engines are not unlike your others. They like 32-34* total mechanical advance all in. You'll need a dial back timing light. So depending on how much advance is built in the distributer you will set your initial at 8-12.
I didn't even bother setting the initial on my 68 travelette that has the same 304, simply disconnected the vacuum advance and set the total at 34. Runs great.. Gets 14 -15 on the highway and no pinging at all on pump regular.
Point gap should be between .016 and .019. Set the point gap first then the timing.