That's the problem, Dave. At the time of the track day 4/4 in 2009, it was a different axle from BTR. The crownwheel was smaller in diameter. For this old axle, there was 1:4.1 and even 1:4.3. Günter Biener (first P4SS and then Babydoll) had this options, as did some 4/4 drivers here on the forum. Lost Simon explained it in a post exactly ca. three years ago that the newer axle from around 2012 or so on with the larger crownwheel in diameter had no alternative transmission, only the 1:3.7 crownwheel.
But I'm still hopeful. Craig (former sand color 4/4) was kind enough to send me a PM that I should ask Richard Thorne about the 1:3.9 diff.
