Ok bit transitioning....had to do lots of this with my gelding...He started on a snaffle and ended up on a light weight solid shank low/med. Port bit. I had to switch because he turned into a knot head and absolutely would not listen to his snaffle anymore...
I started by switching to a TT...that worked for a while but he started throwing his head so I decided to try a basic grazing bit. All my friends used them...it has regular shanks with almost a strait bar...sort little bump in the middle not really even a port...that worked fine for a while too but then he wouldnt stop and it was a bit heavy so I switched to my current bit. He tranistioned through all of them withing a few months and is now perfectly happy with his little curb.
So this is the order and pictures of the bits I went through:
As for the transition to neck reining I taught my boy in four days flat...really it can be done!!!
Start on the ground with nothing but a halter and a long rope tied like reins. Step back out of the horses point of view and use the rope to neck rein them over in small circles, if at first they don't get it pull their head too but only long enough to get their feet moving. After they do maybe five circles with just neck pressure stop and relieve the pressure. This is their reward for actually doing the neck rein, no more pressure. Then start up again and work until they do it consistantly. Once they are turning circles with just the pressure on their neck not pulling their head switch sides and start over doing the same thing. This makes up day one.
Day two refresh the ground stuff with about ten circles each direction then in a roundpen or small corral mount up with just the halter and rope still. Walk around neck reining the horse both ways, pointing his head when needing to with the direct rein again but try to use nothing but the neck rein. Once the horse understands it at a walk work at a trot. Do the same thing as when you walked, its just faster now. Once your horse is comfortable neck reining in the pen move to ride the pasture neck reining, still with only halter and lead rope. This makes day two.
Day three you go out with the bridle and bit and all start on the ground again. By using the halter first you built up a base in your horses head of what the neck pressure meant without any confusion. Now with the bit he may start out confussed but he still has an idea. After working ground work just like day one he will understand better and not be confused. Just work like you did on day one until he is good on both sides with the bit. That closes day three.
Day four is just a repeat of day two only with bit and bridle. Ride until he gets it in the pen then ride around the pasture neck reining. Im highly positive your horse will know how to neck rein at this point.
Now my horse is hot headed and he didnt like the switch from direct reining to neck reining. Once he understood the concept I just had to ride him lots and make him do it over and over. Now he flips like a charm!
Also it will help if you complete your bit transitioning first! So what ever bit you decide they will be ridden on is the one you need to train the horse with.
Hope all of that helps you with your bit transitions and your neck reining!