Mating a 4 speed to a slant, question on years

There is a very confusing issue with the slant six crank between 67 and 68. The size of the hole at the end of the crank changed. The flywheel from one will not fit on the other engine. Its a huge problem on automatics but will also be a pain on standards. I am wanting to say the newer flywheel hole will be too large to fit properly on the old crank and that you will need a 67 and down flywheel. CharrlieS is very knowledgeable on this and there are several older posts which I will look for and repost