It is easy to have A/C in your LS engine swapped Porsche. You don't need a special compressor or wiring. The Porsche A/C compressor is a simple one wire unit. The car just provides 12V to the compressor clutch when the HVAC controls call for it. The compressor is grounded through the bracket.
We have found this Holley 20-160 Low A/C Compressor to be the best option for the A/C compressor. Other kits that mount close to the engine and low can also work.
Make sure you properly discharge the A/C system before you work on it. It is best to take the car to a shop to do this if possible.
You will want to leave the Porsche A/C hoses going to the compressor as long as possible when you cut them. There is no easy way to remove them from the car, instead the best option is to splice into them while they are in the car.
If you want to splice the hoses yourself, this Mastercool (71550) Black Manual A/C Hose Crimper works well.
To splice it into the Porsche system you need the following are the parts numbers from ColdHose.com or other A/C shop.
# 10 - # 12 (1/2" - 5/8") Barrier Hose Inline Splicer RB6107
# 8 - # 10 (13/32" - 1/2") Barrier Hose Inline Splicer RB6106
# 8 90 Degree O-ring Fitting RB1322
# 10 90 Degree O-ring Fitting RB1323
# 8 (13/32") Reduced Barrier A/C Hose Per Foot Length 5 ft RBH8
# 10 (1/2") Reduced Barrier A/C Hose Per Foot Length 5 ft RBH10
The 90 degree fittings go to the compressor and the splices go to the Porsche hoses. You may have to trim the outer coating of the Porsche hoses to get them to fit in the splices.
Alternatively, an A/C shop can do the hoses for you or a mobile hose service can come to your car to do it for you.
While we are talking about accessories, the ICT Billet LS Alternator Bracket Low Mount Compatible with Chevy Corvette work fine with most LS alternators and will mount it low and out of the way.