Slant sixes are great!! Run forever and are basically bulletproof.
Slantsix dot org has an hei conversion, plus the part # for the extended tip plug. The plug alone is an improvement, the higher curved hei spark adds additional burn.
I converted my God-daughter's Volare slant to a super six 2bbl with hei and those long reach plugs. Made the throttle response waaaay better.
My buddy drives a 72 valiant with the mopar headers and the super six setup, also with the hei. Peppiest little slant I've had the oppotunity to drive. I was impressed.