I'll second what Jorge and JWP said. Try the 270TSX and see what happens. Personally, I have opted to use the 300 gr. A-frame in my .375 H&H rifles, but the 270 TSX would work great, I think.
A Trijicon scope makes sense, IMO, and they do seem to perform great, but keep in mind that lots of buff have been killed with the good ol duplex reticle scope. You might be better off saving the money on a scope and putting it towards something else. Your Nikon might be just fine. One thing I'm a proponent of is larger objectives on Dangerous Game scopes, rather than the "classic" 20mm objectives that guys like to put on their rifles. Especially if you're hunting in the thick bush or in low light situations. That's why I have the 1.75x6x32 Leupold on my DG rifles, rather than the smaller ones.
I don't like the idea of a bipod on a DG rifle. Heck, most PH's don't like slings on DG rifles, so having a bipod hanging off the forend to get caught on everything doesn't make much sense to me, plus it adds a bunch of weight that you have to carry as well. I'd just prepare to use the shooting sticks that your PH will have and leave it at that. The likelihood of a sitting or prone shot while hunting the bush is small anyways. However, if you want to do it and your PH is in favor of it, who am I to tell you differently.
I've got a long neck too and have found that the Winchester Safari Express rifles, with the raised comb, fit me very well. I would guess you could get something similar in a McMillian to fit your Ruger.
As for practice bullets, just buy whatever cheap bullet in the same weight you'll be using for real and use those. If you're shooting off hand or off sticks, precision isn't the name of the game, so as long as they land somewhat close to your other bullets, you'll be good. As you've already indicated, practice is what is important.
All of the above is just my 2 cents. Of course, do whatever makes sense to you and also what makes you happy. Remember it is your hunt, so do what you want, not what every one else tells you to do.
