washandwear you have got it backwards, he wants a extremely tight choke, not a open choke.
A normal Perazzi has a bore of .720 to .730. If he wants a .640 - .650 bored choke tube then you would have a restriction of approx. .080 !!! My Kreighoff K-80 TS has been custom choked by Tom Wilkinson (not screw in chokes) is .034.
Is this going to be a card shooter or turkey gun? I have never known anyone to use a choke this tight for trapshooting. You might call Tom and ask him if he would make you a custom screw in choke, he does make custom screw in chokes for clay target guns. Costs would be pricey, so be prepared. Tom's Phone # is 919-603-0167.
Tom Strunk