Electronics International Tachometer

I have been looking for some time for a more accurate approved tachometer for installation in my Aviat Pitts S2A aircraft. This early Pitts has an undampered Lycoming IO-360-A1A engine that has specific RPM restrictions between 2000-2350 rpm and the factory installed analog tachometer has a clearly marked yellow arc at that range.
I found a used Electronics International R-1-4G30Y200G230R270 however the AML list for the Pitts calls for a R-1-4G30Y200G236R270. I emailed Electronics International and they assured me that the conversion was possible and quoted me $55 for the changes.
I sent the tach to Electronics International and after a few days I got a call that my tach was good but had the old small display and they up-sold me to the improved display for $125 total cost.
When I received the unit all looked good however the model is now a R-1-4G30Y200G235R270 not the R-1-4G30Y200G236R270 as I had initially requested. After two phone calls to tech support they insist that the radial lights are only advisory and that the model designation is not important ? I attempted to call the Seattle Aircraft Certification Office that issued STC SA5924NM however nobody answered. How can this be when the original installed tach had a clearly defined yellow operating range ? Is this tach legal to install in my type certificated aircraft , the model number does not match the AML list?

EI has sent me a letter stating that the instruments I intended to install, a UBG-16 and an OPT were inadvertently left off the AML and would be added to it the next time it was revised. Got a similar letter when I installed gap seals on a friends F-35 Bonanza (they were approved for the C, D and G models). The Hillsboro, OR FSDO said that was OK. I included their letter when I submitted the 337.
Larry Lowenkron
Bellanca Cruisair 14-13-2