re: G19 or G26 for IWB Conceal & Carry?

No offense, but your method makes the grip of the G26 just as long as G19 ... but you still have the shorter barrel of the G26, which results in significantly greater muzzle flip than you'd have with a G19..

The dimension that makes a handgun harder or easier to conceal is the length of the grip ... not the length of the barrel (assuming you're not carrying in your pocket).

With IWB or OWB holsters, the barrel is pointed down alongside your pants leg. So the barrel length is essentially immaterial.

Just buy the G19, get the 16 round capacity, and take advantage of reduced muzzle flip that translates into faster shooting.

If you carry a spare mag, you can add a Glock factory +2 base pad to a G19 mag (to get 17 round capacity in the mag).

Or, if you want even more ammo in your spare mag, get an Aredondo +6 base pad and add that to your G19 or G17 mag.
LINK 1

LINK 2

Both the factory +2 base pad, and the Arredondo +6 base pad, eliminate the issue of having a "skinny" mag extending below the mag well. There is no "gap," nor is there a "bare mag" hanging below the mag well.