Chainplate Design

[BillShuman]

I am having new chainplates made for my Bayfield 40. On the old ones, the pin hole is obviously too close to the end of the chainplate. What is the rule of thumb for the amount of material between the hole and the edge of the chainplate? They are being made of 3/8" thick 316L. The pins are 1/2 and 5/8 inch.

Also, the old chainplates (which are attached to perpendicular FG knees) just used 3/8" bolts with washers. There are six bolts per chainplate. Do I need to use backing plates in this application or are washers adequate? Thanks.

-Bill