Your Vintage Folbot Super is an excellent sailing kayak. We have configured a BSD sail kit to attach to the washboards. The installation is simple and involves two 1/4" fast pin holes drilled through the washboards to mount the BSD cross tube and then fastening a BSD mast cup to the keelson. The preferred location is just aft of passenger seat. You may also want to order a Long Haul Center mount Board. We have found it to add simplicity, organization and structural integrity with out drilling through the wash board coaming.
You can use your existing rudder but we highly recommend our balanced LH Sailing Rudder Kit. Due to variations in Folbot designs you may need to modify the cast stern rudder mount on your kayak but they often work as is if the hole diameter is 1/4".