I did the LGT-SS700 5-speed trans. I really like the overdrive, and diphram clutch, but install was a pain. Did have to cut top of tunnel for shifter and the T-bar brace in the tunnel for clearance. The speedometer cable still comes out at the crossmember, so clearance is a problem there too, but it works. I don't know what the best overdrive option is if you want to maintain the stock trans tunnel?
The kit I received was supposed to fit, but what they did was use a trans crossmember that dropped the back if the transmission down about 1.5 to 2" from stock. This tilted the engine back to where the headers were hitting the suspension, and the air cleaner was tilted too. So to get it to fit, had to cut T-Bar bracket inside the tunnel to get the trans output back to stock height.