Yeah, too wild for ur application i think! Go something smaller, something to at least avoid head machining for clearances. Then advance up that inlet cam alot maybe to the max, and enjoy possibly 500rpm better response, ive seen it on a built gtr with -10s.
Generally the larger the engine the more tame an equivalent cam will be to my knowledge, ie a big rb25 cam will be even bigger and lumpier for an rb20, it comes down to cc's per cylinder basically.
rb26 and rb27 tho, not sure ur gonna get too much difference, head work would probably influence cam performance more than an extra 100cc. redline in both ur rb27 will be similar to the 26 i'd assume.
if it was an rb26 vs rb30 hybrid question, its a tough choice for cams, u need a decent size to breath with extra cubes, but cos it wont rev hard without big dollars, the cams might be in vain cos the profile and duration is more for top end!
Sorry bout the rant, tried to keep it simple. just my 2c.