Another surprise.

You see those raised areas I spoke of under the heads? That is your pressure distributor.If your washer does not fit tight to the shank under the head next to that pressure pad, Do Not use them in any case no matter their shape.
Clean out the threads in the block and screw down the bolts by hand, every one of them, and make sure the exposed length of the bolts is less than the height of your maincaps. If they are not, then the bolts are too long. If they are more than, (I'm guessing) ~1/4 shorter , then they may be too short.
The top expanded portion of the bolt, under the head, is to align the caps to the block, therefore the fit should be fairly close; snug but not tight.
I'm kindof leaning on; for peace of mind, I would order up a set of ARPs. I got too much invested in my engine to gamble it all on unknown mainbolts