Original examples of those particular clasps should not present a problem, original medals are certainly worth a degree of restoration, but, it should always be offset against costs incurred, at the end of the day, medals to the three regiments that formed the Brigade are not rare, whilst you can replace the original clasps, you cannot replace an original rivet and a restored medal will never be as good as an untouched original.
That is something that only you can decide, if it were me, I would take into account the price actually paid for the medal itself, the cost of the clasps, the cost of the restoration, the fact that you would still want McCaw's KSA, if it remains extant and finally, a comparison, in terms of money, with the cost of a pair of similar medals to another recipient within the Guards Brigade.
Thanks for the reply, I have decided to try to do the best in the restoration, After being in the military and having my own medals I would want someone to do that for me. Thank you and I am extremely grateful for your valuable help. Will report back soon and if there is any more info you can provide will be helpful.