Turbochargers are limited to two turbochargers only. Single turbos are unlimited. For multiple turbos, the inducer bore on the atmosphere compressor housing(s) may be no larger than 3.0 inches measured at the smallest diameter area of the compressor wheel. A bushing may be used to downsize the compressor housing ahead of the wheel. If a bushing or stepped cover is used, the bore must be round, at least 3/4 inch long, mounted within 0.050 inch of the compressor wheel and the inside diameter of the bore may not exceed the 3.0 inch limit. The inducer bore will be measured using a 3.05 inch plug. All provisions allowing air to the wheel other than via the bore are prohibited if the atmospheric turbo is not a true 3” turbo, meaning the compressor wheel protrudes into a 3” inducer bore with no step, clipping, bushing, etc. Stock MWE grooves are permitted on true 3” atmospheric turbo(s). (2011)
It looks to me like a bushing or stepped cover is legal with a MWE grove in a single setup, but not in a twin set up like I had last year. The changes you made are further holding back twin set ups with your clarification. And to make things worse the final say goes to the tech official which is guess who?