so I'm putting together a sidedraft set up and am quickly realizing that allen head bolts would be the way to go. I want to use them on the intake mani to engine connection as well as the intake mani to carb connection. Here is what I'm looking at on McMaster Carr but unsure of pitch and length

Pretty sure m8x1.25 is the way to go...

McMaster-Carr

any suggestions? The set up is a dellorto 48 dhla on a 13b 6port with a one piece "rotary shack style" intake manifold

 

That is correct. The only question is length.

 

I ended up ordering a few lengths 20, 22 and 30mm in length. They only come in like packs of 50 so I will have plenty left over lol.