Header fitment rant, Doug's
You might be right.
I'm retired sheetmetal, specialized in welding. It likely won't be fun, but it will fit.
LOL. Yep...it won't be fun. The biggest thing is, as I'm sure you've already seen is there just isn't room for much anywhere. And the bigger the tubes, the worse it is. One set I did was a set of 1.875 tube headers with a 3.5 inch collector. I made up new cuss words for that. But it only got worse. The next set for that car were 2.125 tubes with a 4 inch collector. Pulled my hair out on that deal.
Both turned out very well, and fit. I could get to all the plugs, and installation was relatively easy. I've built two other sets with 1.750 tubes and it was better. But damn. Still a nightmare.
As a suggestion, to make everything easier, and make installation easier I'd never ever build a set of headers that didn't have slip on collectors. Ever. All of my headers had (and still do) slip on collectors.
If you do that, you can have three seperate sets of tubes for each side. Obviously, you'll have the 3-5 and 4-6 cylinders with two tubes each, but it makes installation much, much easier.
Also, I always took copious notes on how the tubes were built and in which order. That way, when I had to install the headers, you will know what order they go back in. Makes it simpler for sure.
Slip on collectors are the only way I'd do it.
Good luck.