Garry,
I've fitted a full set of Rares door rubbers to my FC & it took me a couple of attempts until I got the right knack (already had the left one
). I'll agree the rubbers aren't exactly the same as the original ones but are nevertheless pretty good and don't need trimming in any way.
You should expect the door will need adjusting as the new rubbers take a while to squish down. I didn't need to re-adjust mine for ages after.
You do need to make sure the channels are cleaned out of any old glue & crap. I found the special "difficult rubbers" glue made by Loctite that Rares sell is just the "magic" you need to get a good fit. You only need a pin-head drop every 100mm or so and if it's done on a warm day it will stick immediately so you need to have a practice fit first.
I would assume your main area of concern is where the top edge of the front door curves over. If not fitted properly about 150mm of seal will bulge out between the door & body. The original rubbers had a different profile for this part and would sit flat against the body a lot better. I found that if you curl the outer edge of the seal over in the direction it should sit and use just the slightest amount of glue to stick it down, then after a couple of months it will stay flat & you can break it away where glued to get a better water tight seal. Hope this helps