I've used a constant curve mast in an Atlas and it felt noticeably different compared to a flex top mast. With the CC mast the sail felt jerky and heavy. I couldn't find a sweet spot playing around with down haul and out haul.
Apparently going the other way isn't as bad (flex top mast in a hard top sail). On a surf trip a buddy had to use a NP mast in his Severne Blade. He said he could feel the difference but it wasn't terrible.
I've used a severne gorilla in a pryde alpha before, functioned fine. From memory Its race gear that will be completely dysfunctional with the the wrong mast.
I guess its down to why youre looking to combine the two. If its because one of them is selling at bargain basement price, it might be worth a shot. If whatever youre buying is top dollar then probably not worth the tryout.
fortunately most sail makers are going to CC
joewindsurfer.blogspot.com/2008/07/masts.html
in the past Severne and NP were at the opposite ends of the scal
hardtop and flextop
if a sail is cambered, you better have the correct mast
if it is not cambered and you are not racing, one can rig "to make it work"
but once you put the proper mast on the sail rather than making do -
you WILL notice the difference
NEVER downhaul so much that the sail is "twitchy"
all depends on you and what you want
if you are buying - rig it, step on mast foot, uphaul it , flip it, etc
GOOD LUCK !!