early A-BODY 1-5/8" x 1-3/4" SMALL BLOCK STEP HEADERS

here is what ttI said about the oil filter adapter issue Mod .
"Can use OEM 90º adapter or REMOTE MOUNT OIL FILTER"

Note: 90º Oil Filter Adapter Bolt: Oil filter adapters are supplied with either a 3/4" or a 1-3/16" hex head mounting bolts.
If your adapter came with the 1-3/16" bolt, modification will be required by machining bolt head to .175 thickness.
[See FN21 for illustration]