Go easy, I have no idea what I'm talking about when it comes to "technically advanced aircraft" as they relate to 91.205 and exprimental category aircraft. considering a "builder assist" EAB situation in the next year or so. They told me they could build an IFR panel on a tandem taildragger in a brief sales discussion, didn't hash things out in detail. I just want to expand my knowledge before furthering the discussion with the manufacturer. Would the 10.6" G3X touch PFD/MFD and a GNX375 (which is an IFR GPS navigator and ADS-B in/out 1090ES transponder) be sufficient for legal IFR instrumentation in an EAB aircraft (enroute nav and RNAV approaches to LPV mins)? I would most likely add a G5 backup instrument for safety, but would that be required by regulation? G3X alone seems to include all the instruments required by 91.205. This manufacturer prefers to use a separate radio tuning head, a GTR-200 for the VHF comm radio, stating that the G3X can be cumbersome to tune by itself. Panel space is at a premium. Would a GTN-650 be more practical than the GNX375 since it could function as the radio tuning head? I have minimal use for a VHF nav radio as included in the 650, and a seperate ADSB transponder would be required with the 650, adding cost and weight. Normally they just equip with a G3X and GTR200 radio tuning head, optionally a remote mount ADS-B transponder, which of course isn't IFR approved due to lack of IFR GPS navigator. No, IFR would not be my primary mission or even fall within the "90% of your mission" rule, but if IFR capability could be attained for just 2-3% additional cost and ~10lbs of weight, it seems prudent. Thanks for any insight.