T3 turbo questions

hi, i have an 88 turbocoupe 5 speed, i want to upgrade to a T3 and saw several, my first question is are all garret t3's going to be able to bolt up to my 3 inch downpipe? or will only some t3' turbo's fit.. also what size of t3 should i go with, a buddy of mine has a T3:compressor A/r is .60 and turbine A/r is .63 is that too big? how much do these cost to rebuild? thanks

------------------
~ITaliano~