If you are going to bend his neck when you get on, you need to do it toward you, so if he does go to move, his hip is AWAY from you, rather than into, and over you.
For teaching him to stand at the mounting block, use the sending exercises to your advantage. Do whatever ground work you are going to before wanting to work on mounting, and then take him to where your block is: I would set it fairly close to a fence, so you can 'squeeze' him between it and the block, via sending exercises. Do that over and over til he is relaxed, then start asking him to stop next to the block...at first that is all you will do; have him stop for a second near it, give him a pat, before sending him off again. (make sure to stop him near the block on both sides, so you train both sides of his brain). When he is comfortable doing that, start asking him to stand there for a little longer, while rubbing him all over; at this point, start stepping up onto the block when you stop him. Send him off again. When he is comfortable with that phase, start having him stand next to the block while you flap the stirrups, pull on stirrups, tap on saddle, etc. Send him away again. Now when he comes to a halt next to the block, do your flapping, slapping of saddle, etc, and then put some weight into stirrup before sending him away again. And so on and so forth, until he is calm and relaxed with whatever you are doing near or on the mounting block, including getting on and off. Approach/retreat, sending, etc... The horse could catch on in a matter of 15 minutes of doing this, or he may need several sessions to get totally comfortable with the process...take it at the pace you feel he needs, in order to 'get it' fully.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."