If you are set on replacing them with CB design, a 15 x 7 wheel will do the trick, and a set of 20/21 x 7 tires will work/look great.
I am sure that you are aware that you will need to change more than the axles to make the change to 3/32 set screw wheels.......you will need to replace the bushings, (single flanged 1/4 x 3/32) ,and you can either sleeve the current crown, or buy a new 3/32 sized crown.....if you use a "modern" crown (Slot-it etc.) you should change the pinion as well, as the stock one is likely a 48P pinion, and while it will work, it won't work well.
If you are trying to achieve a "vintage" look you can buy 15 x 7 wheels/ tires, and Porsche inserts from RSSlotracing..............the attached pic. is of a Strombecker RS 61 with RS wheels/inserts.
Cheers
Chris Walker
