The reel above has a spare cowling thats got a cutout too allow finger pressure too be applied too the rotating winding cap .it gives control when trotting and when backwinding ,you can let go of the handle & still apply a breaking force leaving your other hand free too either steady the rod and apply pressure while you net the fish or keep feeding whilst playing the fish .
i have two cowlings one modified & the origanal one ,i have the same arrangement with one of my mk1 507's
first thing too do is get hold of a spare cowling probably off the online auction site (E-bay)
then you need to check for correct location for the cut out window ,by holding the reel and seeing where your index finger comes too rest on the cowling ,then mark out a line a cm above and below your finger too set the comfortable width so just the pad of your finger will have un restricted access.
the the height of the cutout window has too be just below ( 1mm ) of the pick-up pins and 1mm below the winding cups lip.
a dremal makes the job easy to cut out the window ,otherwise you'll need to drill and cut it out with a hacksaw blade
then you file the ruff edges ,and make them smooth
then you double check the fit (too late now if you've cut in the wrong location)
takes a little practice in use ,dabbing the finger on too slow/brake the (winding cup) spool like you might with a centrepin .but once mastered works a treat .