#1
Does anyone know what amp/ amp settings/ effects he used in Thin Lizzy. I am looking for this "Tight" kind of overdriven sound.
#2
don't know his exact setup, but to get that really great crunchy-yet warm sound, your going to need to get a gibson les paul and a marshall amplifier... I'm not saying you can't get that sound without those things, but I think that's the simplest answer to give you that will make you sound like him/ Scott Gorham/ Gary Moore type of sound.

Your going to have to experiment with the amps to get the sound you want, but Marshalls are very warm but they've got a bite to them... LP's are very warm and thick sounding but you don't need a LP. If your on a budget, look at Vintage Guitar company they make an incredible LP knockoff for the price.

All of those guys in thin lizzy were straight-up 70's rockers, very little frills, Robertson liked to use wah pedals alot, but I think he ran his guitar right through to the amplifier besides the wah and maybe a delay pedal.

Best of luck hope that helped! Picking amps and getting a tone you like is totally subjective, when you find an amp you like (as well as a guitar that YOU HAVE PLAYED through the amp preferably) go from there. I don't want to tell you which amp to pickup for the reason above.
#3
Like the others said, Gibson Les paul through a marshall. Also have your wah pedal cocked at about 3/4 off the way. You can really hear the wah on stuff like massacre.