I had my Ithaca Mag10 cut down to 26" and threaded for choke tubes by
http://www.ahlmans.com/ in MN.
http://www.brownells.com/ has choke the TruChoke tubes. I'm really glad I did it! I see on their website they have installing 10g choke tubes listed at $99.
My Mag10 is a hybrid version.. as I found a set of deluxe stock and forearm (NIB) and swapped out the UGLY field grade wood... so I have a matte finish with NICE checkered stock and forearm. I no longer having to death grip it for traction.
As for turkey loads, I either shoot my handloads of 1-7/8 ounce of nickel plated #5 lead shot or Federals copper plated #4 lead, 2-1/4 ounce loads. It's my back-up turkey gun; but it's primary job, is by the front door for chipmunks, red squirrels and predators(the large ones, two legged ones that take babies)