Sarco sells a Detective slide that will fit most HI-Powers. I bought one and have been happy with it. It carrys better than the full size HI-Power. The unit is well made and shoots a tight group. The particulars can be found at http://www.sarcoinc.com/handguns.html#fm-hipower .The material below is quoted from their site.
DETECTIVE CONVERSION KITS
No need to buy 2 Hi Powers. Our kits will convert your "classic" or your original Hi Power to a concealable "Detective" size (a modular win). These kits will fit all GP1935 Browning made and F.M. Hi Powers (& probably others we still have to test.) It includes everything you need to do the conversion. Includes complete slide assembly, barrel assembly, recoil spring, guide assembly & slide stop - same caliber 9x19 NATO. The unit comes packed in a sealed hard clear plastic container.
$189.50 GUN149 FFL not required
$179.50 GUN150 Dealer with FFL