Hi Warwick34,
I reckon that you can use a Prone rifle for benchrest but it will be difficult to use a benchrest rifle for prone.
Therefore I suggest you practice some prone and find out from experience what style of stock will suit you best before you decide what to buy.
I expect that any Match 54 will be accurate enough if it is in good condition, but the model of the stock and the fittings like the butt-plate and cheek-piece will make a big difference to whether it fits you and suits you. Also consider the trigger weight that you like and whether the rifle's trigger can be adjusted satisfactorily to it. You may prefer a single stage or two stage trigger. Some trigger models can be adjusted to either, especially the latest ones. Be aware that the Anschutz "Modern Trigger" is not the latest one! It is an older model.
Alternatively, of course, you could buy a cheap M54 for benchrest and purchase another if you do decide to also take up prone shooting. You would not then have to change lots of adjustments when changing from benchrest to prone, which might be on the same day at the same match.
I have a Match 54 I might sell, it is quite accurate and I have the original wooden stock for it. Only the position of the buttplate can be adjusted.
I also have a Keppeler alloy stock which fits it and has many more adjustment possibilities. Of course, the alloy stock costs much more than the rifle!
It would also be possible to use the wooden stock for benchrest and the alloy one for prone, as it is a two bolt quick-change.
Regards,
Richard