The racing programs of KW or H&R offer decent but pricy suspension options for serious racing for the coupe.
If you are looking for an economical solution, check out the GAZ kit offered by BMS. With these options, you should get along without a modification of the rear..
..also heard that with minor modifications, you can install an Alfa (155, GTV??) front suspension..
Hope that helps..
P.S. What mods so you plan at the rear axle ???
1) There are no difference between Coupes and 155 front susp. GTV has a completely another system (double wishbone I believe).
2) I tried to reach KW for some info about smth more serious than KW Var 2 (tried it on Coupe - very civil kit, not for a track), but with no success.
3) I'm planning to convert my rear to McPherson similar to front but with multiple rods (like on Fiar Croma or Delta Integrale).