If the length is the issue, use a spacer or a few spacers which can be made both cheaply and easily from wood, plastic or professionally made ones. If the stock is too low, buy a Beartooth comb raiser, brilliant product, my wife had one on a shotgun she used to own and it worked a treat.
http://www.avalon-guns.com/avalon/Comb-Raisers.html
Phil