First, from a post a while back, no one pulled 20k DPS even with the 30% buff in ICC. For reference, fights in the next expansion like baleroc normal mode had a DPS requirement of ~20k and ~16k on maloriak normal. Even in BIS ICC, outside of niche fights where your whole raid burned down a boss quickly and ignored everything while being in full BiS, you didn't do more than 15k. And typically with the 30% buff, it did not exceed 11-13k. Dunno, just found that irritating.
I think the thing you guys are doing is interesting. I remember another guild did this for ICC (?) last year around the end of WOTLK's lifespan. I forgot how far they got but it was not farther than 7 or 8 bosses. But remember this - The gear gap between wrath blues and wrath BiS is much smaller than it was for this expansion. I would recommend you guys just try with the 496's because that DOES seem doable at least for a good bit. With the 471s, I cannot see you getting past norushen even. The healing requirement is going to be pretty steep since you will go to near enrage even if the boss doesn't enrage himself.
As for what healers pulled back then, in 471 gear, at best you won't be pushing past numbers like 50-70k (with the noru buff ~30% higher). And you cannot sustain that for 7 minutes. And IIRC norushen straight up has a required HPS in the range of ~300-400k, depending on how your raid uses defensives etc. But if you guys 3 heal it, you will probably hit the enrage for sure.
I dunno, I would just make sure your whole raid has a solid set of 496 itemized gear (not the crappy one stat spirit item etc).