This took me two tries to get right. the pics show a 1/4 bolt, I settled on a 3/8 and just ground the shoulder down on a bench grinder after I cut the head off. The length of 2X2-1/8 wall square stock I extended to 2 inches. Use a bearing nut as a welding jig for depth and spacing.
If I make another I might even use 4 pins. If there was interest, Id consider fab'n some up to sell.