I remember coming across Sea Level a while back during my on-going quest to make sure I'm missing out on no awesome pre-me-being-born classic rock. I can't say it made a great impression on me, but then again if I had to point out one apparent difference in our two tastes, it'd be that I put qualify overt "jamminess" as a negative trait, not a positive one.
But if you know what you're getting into (and it sounds like you do), then I can't imagine you being too disappointed if you give them a closer listen.
Another suggestion, if you're looking for semi-obscure mid-70s "remnant" bands: West, Bruce, and Lang. [Lange? I don't remember for sure.] Three guys, all left over from either Cream or Mountain, who bring all the hard-bluesey aspects I love about that era, and keep the jamminess at exactly the right level (phenomonal solos and breakdowns, but they remember that there's rarely a good reason for a studio track to last longer than 5 mintues, too).
I think they might have done two albums, tops, before breaking up themselves. Doesn't matter, because the one you want to look for is "Why Don'tchya?" and has a track called "The Doctor" as #3 on side one. That song is the only time in my long tenure of playing in various bands where I vetoed doing a cover out of pure, unabashed inadequacy as a bassist. And trust me, I'm not shy about proclaiming my great skillz or about reworking a song to be be shorter or simplified, but in this case, if we took out the parts I couldn't play and just focused on the main riff/verse/chorus progression, we'd have had us about 2 minutes worth of song, which just wouldn't have been right.
EDITED TO ADD: It's spelled Laing, apparently. And also: sometimes I forget how good a friend YouTube can be when it comes to pilfering the intellectual property of others. I found "The Doctor" on there, should anyone want to listen to one of the most kick-rump hidden gems of the 70s: http://www.youtube.com/watch?v=CZL32LAtVVA
. I think you'll find the bassing makes you feel as stupid as it makes me feel.