Welcome Mwilliams. I am doing a 55 1st series and the bolt kit I purchased from LMC had 5/16" coarse thread bolts which is what I took out of them.
56 may be different that's all I can tell you. Try different size bolts untill you find the right size that will fit the hole. Bare in mind that the holes are made bigger for alignment purposes.
Good luck with your project! We love pictures!