Just bought a replacement WOT4 ARTF after losing old faithful due to suspected radio interference and have come across the same problem as yourself. The old mount was slotted and adjustable to suit the dimensions of the engine. With the new mount fitted my poor OS 35FP just drops straight through so tonight I will try enlarging the rear fixing holes sufficiently to accommodate without losing it's structural integrity. Have noticed there seems to be a few other production changes since assembling my last one a couple of years ago.