You need a 4 mill serval or 4 mill stock ported cylinder. HJR can do a solid port job on stock cylinders. Have a sponsor put it together for you if you have limited mechanical skills. You will just have to figure out carb tuning or take it to a dyno.
280 main is lean unless your riding in high elevations. My t5 bike without porting, vf4, milled head, and plus 4 timing at sea level is at 300 main. I would start with a 320 on yours.
You could do it yourself and get little to no gains and possibly destroy your cylinders or you can send them to a site sponsor and get guaranteed results simple as that you choose.
We've ran the toomey needle in my bolt on stocker since new. T-5's, milled head, +4 timing, and pods. It has 32.5 pilot and 300 main and it runs great in Glamis and always has.