I can second/third/fourth/fifth (sry about the pun) the TKO600 suggestion...I also have the 0.82 final drive with a 3.54 rear (equals a 2.90 total final drive), but this is with a small block 347, so I refrained from posting my opinion when you guys are more knowledgable about FE characteristics/happiness. In any case, with 15" Trigos and 275/60 tires, I am at a very civilized 2500-2800rpm at sane highway speeds. I went on a 1200mi trip last year and achieved 17mi/gal (again small block with 44 IDF's) on average and this was with shorter tires - 295/50's.
The only issue that I've discovered with the TKO is slight grinding into 3rd on quick up/down shifts. I've experienced this on large auto-x courses and at the strip. A quick google search also shows others have had the issue, but under normal driving conditions I never experience it. In summary, I'm very happy with the gear spacing and quality of the gearbox....it's relatively light, too. I just had mine out this past weekend fixing a flywheel ring gear issue.
- Allen.