For the top Hi-Power experts in the good ole US of A, I'd look over
www.AmericanPistol.com www.Browning.com (the custom shop) Karl Sokal's Chestnut Mountain Sports in VT or maybe Cylinder & Slide in Nebraska.
Sokal is highly rated & did Hi-Power custom work for many LE & spec ops in the 1980s/1990s. The FBI's elite HRT(Hostage Rescue Team) used Sokal's shop. At one time, each HRT member was issued 2 Hi-Power 9x19mm sidearms for duty use.
ClydeFrog