Many, many thanks for the useful comments
I've done some dry practice in the park with the 40+ and got a bit better at controlling things (although i always seem to do better in the absence of water and fish!)
I guess if I was going to cut the head down I'd have to cut at the existing join, trim from the rear of the head and then join again, as with a standard shooting head when adjusting to rod and personal preference.
I think the best thing though, is to find myself a casting instructor and - amongst my other multiple faults - have them take a look at me chucking the 40+.
I think got to a point where some expert observation is what I'd get most out of ...
Thanks again - I really appreciate your answers!