TRX 350 d rear end, into a TRX 300 2x4

there are numerous ways to make the bracket to hold the new rear end to the swing arm , some just make a flat plate , and cut hole in the middle of it and then slice it in half , then drill holes to attach it to the swing arm , then weld it up , the way I do it is use the center section of the oem 300 rear end , which you say you don't have , you can buy the center piece off e-bay for about $20 and to me it would be worth it , for two reasons , one to make a strong mount and to make a shock mount , as mentioned you need to weld in a single shock mount in the middle , in the pic you can see the saddle with the shock mount is a cutting off the 300 center section , makes lining it up and welding go much easier this way ------------------ other things you will encounter , if you use 12 inch wide rear wheels then you will need 1 1/2 to 2 inch wheel spacers to clear the muffler , even with 10's you will most likely need a 1 inch spacer , the foot brake cable "may "have to be longer by an inch or two depending on the combination of model year 300 and the model year of the rear end you are going to use