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I went with this company since they are local to me:
http://westcoastriots.com/shop/automobile-machine/m54b3-0-engine-big-bore-throttle-body-bmw-p-n-13547502445/

No dyno results, but given that...

I can confirm they work. I installed a pair of 90deg angled extenders on my ZHP with catless headers (in the rear-most bungs). It is a bit of a struggle to get them to fit, lots of initial loose...