Its hard to say, especially with the size. If it was a medium or other common size and all original spec i would be looking for at least £1000. The thing is, to get it to original spec could be quite costly as it was specced with top end and still desirable kit. Some consolation is the kit on it now looks quite decent so you should get some money for that to help fund the restoration.
There is plenty of info online about them and you may be able to gauge value and desirability from reading through some of that also.