The flat roller ider gear is no longer available. You can only get the roller ball bearing style idler that uses the single large bolt through the middle. The replacement is a SBC part.
My mounting plate uses two bolts other than the two behind the cam gear. For the bolts at the bottom of the plate, the one nearer the idler gear is 1/4-20, and the other one is 5/16-18 x 3/4 and is located opposite side of the plate of where the idler gear is. They are both allen socket head cap screws. They both thread into the block.
I don't remember the sizes behind the cam gear. Those are both button head cap screws. If I recall correctly, the size of the button heads behind the cam gear are larger than 5/16". I can check for you when I get to the shop.
My mounting plate uses two bolts other than the two behind the cam gear. For the bolts at the bottom of the plate, the one nearer the idler gear is 1/4-20, and the other one is 5/16-18 x 3/4 and is located opposite side of the plate of where the idler gear is. They are both allen socket head cap screws. They both thread into the block.
I don't remember the sizes behind the cam gear. Those are both button head cap screws. If I recall correctly, the size of the button heads behind the cam gear are larger than 5/16". I can check for you when I get to the shop.