400ex swingarm on a 300ex frame.

ok I aquired a 300ex frame recently. and a bunch of parts. one of the parts is a 400ex axle. but when installed into a 300 swingarm the bearing race or whatever its called ois outside the carrier and the axle nut cant be tightened. he has a 400 ex and we measured and it looked lik the 400 was 9 a shy 3/8 from flange to flange of frame and the 300 was a dead on 9 1/4. so I figured it would be EASY to bust out the grinder and take a measly shy 1/6th from each flange. but that about the part where the swing arm bolt goes through the engine case? is that the same between the 300/400's? I need to get a swingarm no matter what cuz none is included, not even stock, and Id ratehr run a 400 swing/shock back there if I can.

oh an anyone know where I can get performance parts for a 350x engine?