Haven't had a chance to look at a place yet that would be able to repair the reverse gear, locally would be ideal, thinking smoothing it out might be the best option. My hesitance is smoothing it out too much and then finding it's useless. I assume the mechanical lockout consideration is because reverse is too easy to engage whilst driving?
Yes I found reverse too many times when in a hurry (one was my only time at santa pod).
Reverse gear - I think you just need to make sure that the gears can slide together. Reverse is the only gears where the actual gear - wheel moves into engagement.