Oh do I have a list of things that are a MUST to replace on this bird. First of all, running two of those batteries you have in SERIES, your going to be tail heavy. You need a 6s 3000mah pack. It's stated that a 6s 2650 pack will work, but I had the 3000 as did Lee on here. 3300 would make it a little nose heavy, but with the battery tray mod, should work. But you MUST run this bird on 6s or it will not have enough power and will be very sluggish in the air.
Now onto the parts that you will have to replace. First off, if it's plastic, replace it. This includes the washout arms, mixing arms, any grips for the blades, linkage levers and so on. Replace everything with Align, or at the very LEAST, EXI. Get a good set of servos on this thing, and spend good money on the tail. This bird is big enough to kill someone, and safety is key.
If you search the forum for "hk500gt" you will find my troubles that I have been though, and the maiden flight after I fixed everything. Once things were fixed, it was solid. However, the tail was still drifting because I cheaped out on the tail.
good luck with the build
