You dont necessaryarly need them in the shocks, Jim Dixon said on the
www.the-pred.co.uk forum that they make the car more consistant using them.
Also with youre car being on bumpy tracks the idea of a shock re-bound valve is to let oil through slower upon impact then relase the oil faster back the other way i beleive studying them on a site, so maybe on a bumpy track maybe not using them if they maybe cause maybe a tiny bit more pack making the suspension slightly stiffer upon quick pounding on bumps on hard rutted areas may make the car "Loose" or make the front end rise more, Not using them could be worth a try first off then see how you get on. If you dont like it just pop them in and try it see how you go
I asked about this a good month or so ago if they was needed and i got some helpful comments back on this thread:
http://www.the-pred.co.uk/forum/index.php?topic=332.0
Garry