RamSavageLST has the best way I have seen. Before he did what he did to his I made mine that way using a LOSI shims kit at the suggestion of another user here.
I have about 4 gallons on this setup now...
I used LOSA5050 shock Spacers to shim the shift forks.
My racer tranny
LOSI is coming out with a solution that I will switch to at that time.