Is using the larger thrust bearing stack an absolute must when using the front FD Stationary gear?

Im building an extra Series 4 motor and need to use the s4 front counter weight and s4 front stack with it. Other than the oil bearing oil groove and the machined bevel, both the s4 and s6 stationary gears measure the same. The width(non beveled portion) and depth of the land where the thrust plate/needle bearing goes is the same.

Is there something I am missing that would keep me from using an s4 front stack with the FD stationary gears?

Thanks

 

The S4/s5 thrust washer stack will fit just fine, and work fine on the FD gears. I've had to do it for the same reasons you listed.