Here is the page from the repair manual. You have to go to the parts book to decipher the bolt sizes. I've done these bolts and listed them below the illustration.
X = Hexhead
UF = U.N.F.
B = Bolt
06 = number of 16ths or 3/8"
24 = length in 16ths or 1 1/2"
So the rear bolts are 3/8" UNF 1 1/2 inches long
Fronts are 3/8" UNF 1 1/4" long
Dash bolts are 3/8" UNF 1" long
Fire wall bolts 1/4" UNF 3/4" long (except I don't think they are used on the Twin Cam.