I understand how the gear boxes work and I have plenty of them : the problem is I tried many different whisker Kadees (underset, overset and centreset) fitted with gearboxes and none would give the correct height without chopping into the bogie. It was only when I removed the gear box that I found that the #148 was the perfect height. I also tried #17, 18, 19 and 20's and found the same problem of not being the correct height without modifications to the bogie. I did not want to use glue except as a last resort.
I used the #146 with its gear box to convert all my wagons.