I square one end of the handle material, normally the pivot end, and push it up against the bolster and let the handle set on top of the rear bolster. I hold it tight against the front bolster and then mark the rear bolster with a pencil in the liner side. I mark the edge of the material so I can see it from the front side and then mark the front side just a little longer. Cut off the excess and grind a little ay a time until the handle material starts fitting between the bolsters. I use a disk grinder for this.
Test fit often and make sure the material fits flat against the bolsters. When they both fit attach them to the liners and cut off the excess and grind to the edges of the liners.
I hope this explains what you were asking for.
Here is a photo with one fit.
Craig