Several of us tried "high output" aftermarket alternators in years past with very limited success - mostly failure. The control in the LS Gen1 alternator is somewhat uncommon, so the aftermarket just doesn't deal with it well.
This also hits on the usual problem with "high output" alternators. You've fighting physics - there's only so much that can happen. The Ls uses a fairly small case alternator, so getting a higher output rating requires modifying it such that its output during most of its performance curve is actually *lowered*. This is OK for SPL competitions where you just set a fast idle to keep things spinning while competing - but sucks for actually driving the car. I messed around with alternator stuff for *years*, especially with my other cars, and most alternator shops are extremely, uh, creative with their advertising. Yes, hairpins can get a good 20%+ more output than traditional, but anything usefully more needs a bigger case and more copper.
Whether a second battery, or a second alternator, or both is the right answer just depends on what you're doing. Short, sudden spikes only? (e.g. short SPL runs) Second batt is fine. Sustained draw (lots of accessories/fans/stereo going full blast all time)? need a second alt. Both problems - or you're trying to win the regional SPL competition? Both solutions.
Mounting an alternator isn't horrible, just time and fabrication. The thing to watch out for is the PCM fighting the new alternator. The PCM will actually command BELOW 14V for fuel economy when it thinks it's OK. So if the other alternator is putting out 14.2 all the time then the PCM may actually shut down the OEM alternator. I *think* the SCT actually can access the alternator control? It's been a long time.
Realistically, the best choice is to throw away the stock system and put in a simpler alternator setup. The PCM will just complain endlessly about it.