Nice! That is a big step. My feelings on manifolds were similar to yours. The power gain is not really a factor, OEMs are nicely designed and if they fit, run em.
I went with the JTR/Sandersons they are ok. Easy close fit to the block, which leaves plenty of room. The are off the shelf, which saves time and expense. In hindsight I sort of wish I had either went with Hawks long tubes, or made my own. Honestly, mostly because long tubes look cool.
The turbo guys weld V-band flanges to OEM manifolds all the time. Might be worth considering.
I am sure whatever you come up with will be bad ass.