I've already done this :) While I probably have a different body frame (5'10" 165#), I always felt that the LWB did not sit low enough. I have been running custom P1 Designs inserts for the past few years and had the driver butt cushion made 1" thinner so I could sit lower. It made a noticeable...
Have you looked at the Recaro P1300 GT? This is the seat for Cup Cars, what's special is that it has a specific seat rail where the sliders are on the sides instead of underneath. It should allow you to sit lower, but also there are different seat pads that can achieve an even lower seating...
I'm a die hard Recaro loyalist. For your frame, you may want to look at the SPG XL or the Podium (L).
My car came with the OEM LWBs, but honestly they are not ideal for serious track driving. The seating position feels off to me (even with angle brackets) and I wish I could sit lower. I already...
From my research over the years, it seems that only Manthey themselves has the ability to code out the airbag light for 991s. A couple local shops have claimed this ability, however I have not seen any success stories.