It’s a pretty straightforward job to replace the mast foot plug, and this would give you a nice free-moving set of sheaves. Remember that the bolt apparently restraining the foot of the mast isn’t the only thing stopping the mast from toppling forward, so don’t be spooked by the idea that it’s become bent. That can be replaced, then once it’s in what you are sure is the right position, it will last years.
The key thing to remember is that the mast pin doesn’t do anything while the mast is up – it just sits there. It shouldn’t take any strain at all, either when the rig is tensioned or not, provided the mast is upright. A narrow (6mm) pin gives you a better chance of achieving this, but you may well need to tweak the mast step height with packers as has been suggested.
Sort out the plug first, then set up the mast and perhaps even remove the pin, check the mast rake with a long tape measure (follow one of the standard tuning guides). Adjust the position of the new little bolt in the back of the mast step track and see if the holes in the tabernacle line up with the mast hole, with and without full rig tension. (You don’t want the pin to snag or stress the mast in either situation). If the height is wrong you can pack the mast upwards (if that’s the direction it needs to be moved!)
For fore and aft adjustment, with full rig tension the mast is being pushed down really firmly onto the mast step, but a small amount of repositioning is possible. If the holes now line up through both the mast and the tabernacle you have a provisional position for the little bolt in the mast step track. Check that the holes still line up (with mast pin free) without rig tension.
You may have to go through the whole tuning/tweaking cycle a couple of times, but once you’re satisfied with it you will feel confident in yourself and your boat!