Right around 1981 is when they changed the crankshaft imbalance of the 302 from 28 ounces to the ""5.0" style 50 ounce imbalance. That imbalance is critical to flexplate selections. (Flywheels don't flex and are used with clutches, but most folks know what you mean either way.) Pre-1981 302 is the same as a 289 imbalance. A stock flexplate for a 1967 289 C4 Mustang should do you just fine. Although the 289 and 302 are slightly different internally, for the most part they are the same externally as far as bolting stuff to them. With only a few cosmetic differences, 1967's and 1968's are almost identical. Early 1968's got 289's, a few in the middle got sort of 289/302 hybrids, and late 1968's got 302's. So it might make it easier on you to consider your car a late 1968 302 when you look to buy parts. And lie to the parts counter people.
Ford guys go by the number of flexplate/flywheel teeth but the real difference is the diameter. The teeth are the same size so logically to fit more teeth, the circle has to be bigger. The bellhousing is sized to accommodate a certain sized flexplate and places the starter accordingly. So if you have a "big" bellhousing and a small flexplate the starter will likely completely miss the teeth. Generally big flexplates just don't fit into small bellhousings. Big meaning 157 teeth and small 164. Though there are vintage 160 tooth ones, they are considered interchangeable with 157 teeth. Though a little rare, there exist "big bell" 164 tooth flexplate C4's that were used in trucks. Just in case you accidentally got hold of one. You can use one, they're just not common.
When you are spending a lot of money on an expensive engine rebuild, there is a balancing process towards the end where they will want to have your intended flexplate/flywheel at the shop with the engine. Other than that you just buy the correct parts at the store and bolt them on. Building your drivetrain as a 1968 302/C4, I would simply use the correct starter for that car.