SBP DISC to LBP DISC SWAP- 72 Swinger

Need some more help. I got the '85 Diplomat discs to put on my '72 front drum Scamp. I now see that the knuckle on the '85 set up has bolts through the spindle that thread into the knuckle. The '74 knuckles have smooth holes. Do I just get longer bolts and have the nuts against the knuckles? The '85 bolts have extremely flat heads, I assume to clear the discs. If I get longer standard head bolts will they hit the discs? What have you guys done to fix this? I wouldn't want to modify new bolt heads and have them fail.

Stephen Shaw