Changing individual gear ratios?

[CrankyOldMan]

I've looked over the threads on final drive (FD) swap and the much more substantial 5->6 speed swap, but I haven't found any info on changing individual gear ratios.

A co-worker gave me a spreadsheet that helps calculate RPM drops between gears and by looking at some dyno charts it seems that the gap between 1-2 is too far, and the gap between 3-4 and 4-5 are less than ideal. I've also tried to find some coherent info on "shift points" but it still isn't making sense. My basic understanding at this point is: the torque doesn't really kick in until about 4k, and the redline is between 6k and 6.5k, meaning that you want to shift at redline but have the next gear pick up right around 4k to keep yourself in the power band.

All that said, is it possible/practical to alter the individual ratios to optimize them? I haven't dismantled a manual transmission before, but I built a LEGO model with a 3-speed gearbox once, so I understand that there are some important clearance issues with gear diameters.

Assuming that it is possible, it would of course make sense to have this done at the same time as a FD/clutch/flywheel/LSD mod. Your thoughts?