914 legal in a Sport Cruiser?

You might also look into one of the "Big Bore" kits (Zipper or Edge Performance), as they will increase your sea level horsepower by up to 15%, which would give you a good bit of extra power at 10,000' and above. 

There's a video on YouTube (Gravity Knight Flying) where he takes his Zipper-modified Rotax 912ULS powered Rans S-6 to 17,999 ft, and it was still climbing better than my old 100-HP Citabria did at just above sea level!  If / when I get around to flying in the high country, that's what I would probably do for my Rans S-6, instead of replacing the engine with the 914 or 915.

Jon I own CRUZ N614SC.  I have not flown it in the mountains but I regularly fly at altitudes at or above 10k without any difficulty.  I have taken it up to 15,000 which is the limit established in the POH and again, it is not a problem.  You do know that climb rate will dissipate based upon altitude and your gross weight so if you're "heavy" it's going to take a little while to get to altitude, but, the SC is up to the challenge.  I considered the Bristell and the SD4 Viper because they both had the option for a 914.  Propeller pitch, as stated above, was an issue, as was the additional weight of the 914.  Because I fly primarily in the east and most of the time in Florida, altitudes above 10-12k weren't really an issue for me.  I might feel differently if I were flying out west, but, if that were the case, I'd look at either something that flies a 914 or go to an experimental with a TB engine.  I love the 912.  It's reliable, is economical both in terms of fuel burn and maintenance and I have had no difficulties whatsoever with the engine.  The SC is a delight to fly and in spite of its size, is comfortable in all phases of flight and if you slow it down a little, is reasonably comfortable in our hot and turbulent Florida summer afternoons.  Again, knowing that you have a strong and reliable engine up front gives you a lot of confidence that you're never going to have to use the BRS system.