Here ya go bud.
Measurement on the chain is 16 1/2'' long with a center to center of 16" (bolt to bolt).
I used 1/4" proof chain (hoist chain) and covered it with shrink tube to keep the chain from slapping around and smacking tank. It works real well. Actually stole the idea from another member here but just changed the set up cause I didn't like his.
You MUST cycle the rear wheel up and down to make sure you got no bind.
You have been warned.