Dont laugh but i think all the old type 9 gearboxes had the same doughnut, cos i had a 1800 prop and a 2.9 xr4x4 prop and they were the same. From memory a few years ago when i had my 4x4 cos they were the same as. The gaf 31's and 41's are only for 2wd mt75's and they only come complete with prop as they are 'supposed' to be balanced as one unit