canon 100mm teleconverter port extention

am looking at getting the 100mm and at a later date putting my 1.4 teleconverter on it ,is it possible to get only 1 modular port for both 100mm on it's own and the 100mm and converter together, the teleconverter makes the lens 20mm longer would using a port 20mm longer make any difference to the optics and frame coverage? and if ok which port extention would i need to do both? PS:-looking at the AUTO only port extention, any info would be appreciated
Steve

If you're using one of the 100mm USM lenses, they require the 5510.28 which is the longest modular port body we make. You could add either the 5510.54 (19mm) or 5510.58 (31.75mm) extension when using the teleconverter. Check the overall length of lens and teleconverter against the specifications on this page to be sure your combination will fit: MODULAR PORT SYSTEM

Regards,
Jean / Ikelite
http://www.ikelit