Your doubles were caused by use of improper plate cell size. Popcorn seed is pretty small and he used a plate with cells too large, allowing doubles. Common result lots of times even with larger kernel hybrids.
The long skips and the picture of open slits was caused by using a planter with old fashioned runners and no closing wheels in a field that simply was too wet to plant....the seed was planted (with lots of doubles) but a lot of it got exposed to air and light. You certainly had what is called "poor soil-to-seed contact.
The IH 56 planter is a good old planter, but it is not designed for the field conditions you had at that time. Plant corn in soil that is worked up nicely and not so wet. And...get the proper plates for popcorn next year.
LA in WI