You're going to need an adapter/spacer for mating that D300 to your AX15. There are a few places to purchase one from. I got mine from KANROK, and am pleased with it. All it is is a 7/8" piece of aluminum. It's needed because the stickout of the AX15's output shaft is too long for the D300, so it needs to be spaced out 7/8 of an inch. You can use a 3/4" spacer, but then you have to goto a sealed bearing, and I'd rather not go that route to save 1/8 of an inch. Let me know if you have any questions on this swap, as I finished mine up earlier this year. I also made a set of twin sticks for it for about $20 or so.