I was thinking of making some of these out of nylon / plastic, do you think they would be too rigid

http://www.moke.com.au/images/stories/M ... _Reels.jpg

Yep: they'll last about 3 minutes - they're rubber for a reason.
If you want to tighten up the gearstick motion a bit, just put another rubber one in.
I have three on mine - solid as a rock but still copes with the engine movement / vibrations.

Thanks. Thought as much they would be easy to make hence the question.

I will order some new ones as my original are soft, possibly never been changed and they got a tad hot in the fire.

The previous owner of my car did this top notch mod.

You can try exhaust mount ones, they're a bit stronger but still rubber. Don't forget the bushes in housings. Oh, and some mudguard washers might fix your problem.