[unruhjonny]

I believe that the 1973 98cc heads were in fact the 400 heads;
If my memory serves me the published compression for 1973/1974 was 8.2:1.
(vs 1971/1972 advertised compression of 8.4:1, then 1975/1976 compression of 7.6:1)

All that being said though, if the date codes align it wouldn't seem completely unbelievable for 98cc heads to have been used;
I have heard more about 75-77 heads either being different castings/combustion chamber size from left to right - so that doesn't seem like a giant stretch...
But I'll default to believing anyone more knowledgeable in this stuff...

When I had my '73 Formula (350/350 car), the plan was to build it as a 1973 Formula 455, so I sourced the correct 4X-1H(114cc) heads for it;
After I gave the car back to my brother he decided to acquire 1974 4X-4H heads;
The heads he bought were the 98cc castings, but if my memory serves me, after a given date early in the 1974 model year all 4X heads received screw in studs (as opposed to the pressed-in studs that all(?) 1973-4X heads had) - the heads he bought need nothing, as they were previously rebuilt, but swapped out for aluminum heads, and left at the shop.