During disassembly of my engine to resolve my "no oil to rocker arm" issue, I found that instead of a 1 7/16" nut threaded onto the outside of my camshaft to hold the cam timing gear on the camshaft, I instead have an allen head bolt and washer, threaded internally into the camshaft itself. This is a B20 block, piston borings marked "D" (stock?). Was this some specific model year or application change, or perhaps simply an aftermarket camshaft, and if that is the case, who makes theirs like this?