As a fellow Speedtech n55 customer I'm really interested to see how this goes for you. Are you planning on keeping the engine stock? I also am itching for more power and am considering going the external wastegate route. Just trying to figure out if I want to stay in the EFR lineup or not, I currently have a 7670. Subbed.
Edit: Just saw your reply regarding what you'd like to do with the engine if rebuilding. Saw the shops you listed as well. I recommend getting in contact with Billy from BMB Autowerks.
https://instagram.com/b_mase_monkey?igshid=moxograrhaqz info@bmbautowerks.com He has a large portfolio of built N55s, aside from his N54/S55 customers.