[WFBowen]

You have a few options for your 68. For 15 inch rims you can use stock 5.5 width painted or chrome, 5.5 x14 Fuchs which were used on 912E and certain 911 cars with “comfort group” option as well as 911E. Then the price starts climbing with 7” wide 911R Fuchs, American RacingTorque Thrust 7”; one year only 1968 5.5 wide Fuchs; Mahle “gas burners.” For 16 inch diameter. I’ve seen SWB cars running 6 inch wide Fuchs (911SC fronts) all around. Keep in mind that when deviating from original size you might well run into rubbing issues with tires, offset, spacers, etc. As for tires, you’ll want to stay with something in the 25 inch diameter. range. I’m assuming you’re running 195/65r15.
Member cmpski has a SWB car that runs a Fuchs /tire combination that seems to be a solution that works and looks great.