You don't mention your combination (B/RB/LA). I went to Performer RPM's 8 years ago on my stroker B engine. To my surprise, my Hooker Headers were tight as far as spark plug clearance. I believe that the #1 cylinder was the biggest problem. The earlier design hookers were designed for heads with straight out spark plug orientation. The RPM's have angled plugs. I had to make a little jig for my press and dimple a few of the tubes. As I mentioned, the #1 cylinder was the biggest problem because the header tube exits the exhaust port at the same angle as the spark plug end. So the spark plug insulator and plug wire tip ran parallel (underneith) with the header tube. That required a bigger dimple to create clearance for the plug wire connector end. I wasn't about to beat my nice polished ceramic coated Hooker header with a ball pean hammer so I made a tube holder out of wood (oak) and a little metal thick wall tube welded to a tube that slid over the tip of my press. I pressed a dimple into the header tube and then test fit and then pressed some more until I had enough clearance to get the plug wire onto the spark plug tip with a decent air gap. I believe that somewhere around 2004, Hooker redesigned their B/RB headers so that they would fit with angled and straight spark plug orientation.

The other issue I ran into was that the exhaust header flange hit the tops of the ARP cylinder head stud kit. I had to trim the nice allen head end of the stud down so it would clear.

I found a picture in my archive ... you can see that the plugs are in the odd numbered cylinder head and the #1 plug wire is attached. I'm pretty sure I took this picture right around the time I was trial fitting the headers to my new Eddy RPM cylinder heads.