I have one shortened to 4.5" barrel length that was originally an IPSC Modified pistol and my gunsmith has done others at 4.25" barrel lengths, the same as a Colt Commander. I do not have pictures or graphics, but just to get you started, he does the following:
Mark the slide at the desired length.
Use a sharp new hacksaw blade to cut off the slide just in front of that mark.
Use a center cutting end mill on the milling machine to cut the slide to the finished length. File a slight bevel to the corners, like the factory did, or a little more.
Use a keyway cutter to mill a new barrel bushing retaining groove.
Bore out the recoil spring tunnel to accept a reverse recoil spring plug.
Use a dovetail cutter to make a place for a new front sight.
Shorten the barrel to correspond with the slide and fit a Commander bushing or cut off a Government Model bushing to about that length.
In the lathe, turn the barrel to remove the front locking lug and leave it cylindrical almost back to the second locking lug. This is necessary to keep even a shortened barrel bushing from crashing into the front lug in recoil.
Make a full length guide rod smaller in diameter than the standard and make or modify a recoil spring plug to fit the shortened recoil spring tunnel and with a small hole for the smaller guide rod.
Cut a Glock recoil spring to fit the space available in the recoil spring tunnel.
Assemble and testfire. Adjust as required. File or mill front sight to zero. Refinish.
This system works, my gunsmith likes the way it gives a longer slide travel than a Commander for positive ejection and feeding. His personal pistol is of this type.
Another approach is to make a cone sleeve for the barrel and do away with the barrel bushing. This will save the work of cutting a bushing retaining slot and will save the front locking lug of the barrel.
These have been made with regular recoil springs which would save the work of building a rod for the Glock spring, but that gives a weaker spring that must be watched for wear and replaced more frequently.