I do a lot of Euro pens and frequently use a couple of their specialty clips.
The tight fit is due to you making the upper barrel too fat. These must be turned BtoB (bushing to bushing) without any bulgies. Clips on some model pens can be bent or modified but I have found that quite impossible with the Euros.
IMHO, most of the specialty clips do not show up well and are wasted effort. things like golf clubs, tennis racket, music thingy, etc. just don't show up well at all. I do use the Christian cross quite a bit and it looks nice. The Christian fish (CSUSA calls is a "Jonah") doesn't show well so I don't use it. The rifle clip is popular if combined with a cartridge. Doesn't show well, IMHO, but is a good selling item.
Just don't make your Euro upper barrels bulgie and you should do alright.