The stock part on the stovebolts is 5-3/8" in length and 3/8 course threads into the head and fine thread on the rocker stand and wingnut end:


The GM part number is 838336 group number 0.413. Not sure if there is any old stock still floating around . . . my parts master shows this part was unchanged since the 1934 model year.

Somebody is still making these - Jim Carter Trucks has got a kit for 17 bucks