Welcome to the site man!
Nice to see that MuscleRodz has that LS kit for your car.
When looking to 'pick the right LS engine', you need to ask yourself whether having an aluminum block or an iron block is relevant for you.
The iron blocks are a little more plentiful out there (mostly in trucks/SUV's), and they can handle the extreme ends of supercharged or turbocharged power better. (like 700HP+) They'll also be 70-80lbs heavier, and right over the front wheels which is worse for those looking for greater handling. Personally, I think it's worth the time to find the aluminum block, and I think the accessories will look/fit better.
The other difference to bear in mind when buying a complete junkyard or used motor is the placement of the AC, PS, Alternator. Most trucks/SUV's have one style that is kind of tall and high, then there is the so-called 'F-body' and lastly the 'Corvette' layout. I think you'd probably be best served using the 'F-body' style. On many old cars, the low mount pass-side AC mounting interferes with the engine cross-member. Plenty of places make adapters to mount it higher, or else folks cut a notch out of the engine cross-member.
Chevy LS Accessory-Drive - Gen III/IV Small-Block Swap Guide - Hot Rod Network
Putting the engine in place is the easiest part! It's the other crap that can be painful. (finding trans X-member, floor tunnel mods, getting a radiator to fit, Oil Pan!, etc.) Not to mention what Dave noted about overpowering the rear-end.
All problems easily solved by $$$.