Can't see it in your photo, but you should heat the carb base. I have a draw thru, that I built in 1979, and had idle surge, untill I heated the carb adapter with heater water.
PS: My turbo had the seals. It was designed for draw thru.
Yeah right now the carb base is out in the open- I have read about people needing to heat them but wasn't worried about that initially. This was an experiment for me and now that it seems to actually work I intend to refine it some. Surprisingly mine doesn't surge at idle, it just gets loaded up and cranky.