Lightning headers are likely built to order and they make them in 2 widths. I would think their 33” width headers would work, that would seem to leave 1” between them. Tall decks are only 3/8” taller and that’s on a 45 degree angle so they go up a little and out a little. Aftermarket heads sometimes have raised exhaust ports so that could be another factor. I guess it depends on how close the holes are to spec now. If they are on the low and in side it could be tough, if more to the high and out side you might be just right. Either way, when I bought my lightning headers, years ago, I told them where the holes were and they built the headers to them.

I wanted to go the same route on 12 meter with 34" C to C however after doing the math it wouldn't work out or to close for comfort. That was with stellings though. Not only C to C was gonna be extremely iffy it would have required cutting out each side of the lower part of the deck which is already very close with short deck and raised exhaust. Like ezrizer mentioned with the tighter fit lightenings might work just fine. I just wanted to keep my current headers. If there is anyone with aftermarket raised port heads and tall decks with stellings be sure and post.

You could call lightening direct also. There cast are like 3 1/2" wide.

If your going to run mufflers of some sort you might wanna mention that also.