I strongly "second" Wayne at AHR. He built a 450 Rigby for me, and it's a beautiful thing. In fact, I have a Win M70 pre-64 barreled action in 270 WCF that I've talked to him about converting to a 9.3x62 Mauser when I'm ready, and I have no doubt he'll do a fantastic job.
His rifles function flawlessly on delivery (at least in my experience), and he'll be the first to tell you that for the big bore calibers, it's not just slapping a barrel on an action. He goes through and reworks the CZ 550's feed ramp, rails, magazine, etc. to fit with the intended cartridge's geometry so that the action will cycle as smooth as butter and feed the cartridge flawlessly. The AHR trigger is great. It breaks like a piece of glass, and has no perceptable creep or over-travel that I can tell. It's almost like a target trigger on a big bore DG rifle. My rifle also shoots better than a big bore should or needs to as well.
His wood work may not be the fanciest, and I've seen other gunsmith's rifles that have better "aesthetics", but in my mind, his are gorgeous, and aren't so fancy as to make one worry about scratching, dinging or denting the rifle. His rifles have that classic African look to them, and handle well. The one thing I wasn't sure about was having GunKote on my rifle instead of a satin blued finish, but so far I like it. I suspect it'll definitely be more durable in the hot, African bush. His customer service is great, although fortunately I haven't needed to send my rifle back to him. However, Wayne is good about giving advice about weight, barrel length, scope selection, etc. , and is always available to talk. As far as price, the cost of your rifle is on par with what I paid, and $7000.00 is a lot for a bolt action rifle, but you could probably pay $5000 more for a DGR rifle, and still not have one that worked any better for it's intended purpose than Wayne's. Strong statement I know, but that's how I feel.
As far as reloading data and powder, he'll send you a list of bullets and load data that he's worked up loads for in the caliber your buying. As far as powder, he told me that he almost always goes with H4350 for the big bore rifles, as it gives good charge density (no need for fillers), meters well enough, and is less temperature sensitive than others. It's a recipe that's worked for him, and he uses the powder to test, break-in, and sight-in the rifles he builds. I don't know if that will be applicable to your 505 Gibbs, but it wouldn't surprise me.
Anyway, I feel you made a great choice and hope you'll be as happy with your rifle as I am with mine. I think his rifles offer some of the best value for the money of any builder of big-bore rifles that I've seen.