Your model 19 is perfect. Alot of them are shot at the phase II class. Clean up the front half though, you've got to be in the 290s to be able to make the 540 easier.
A little word about practice. LIVE AT THE 50 YARD LINE! Once you can keep your shots in the 8 ring consistently from the 50, the 25 yard line is no problem. Don't worry about the 25, just practice the 50. The 50 can be a little intimidating, but the 540 is alot easier once you find your consistency.
Here's what I've seen while assisting at the school and training other officers for the school. Get as close to 300 as possible on the front half, and shoot the back half without any zingers(make all 24 rounds score). Then put all the last 6 in there, and you've got it licked. Generally, if you shoot 295 or above on the front half, and make every shot score on the back half, you're up over 550!
Don't worry as much about equipment and grips, as long as the speedloaders will not hang up on the grips. The secret is keeping the front sight in total focus, and squeezing the trigger while not disturbing the sight picture.