2nd gen Firebird/ Forgeline TA3 18" help?

[Tuomas]

Hello,

I have 1978 restored Trans am looking for small lowering in combination Forgeline TA3's in 18".

Purchased ridetech streetgrip kit should lowering approx 2" and it's on way in US and I'm overseas so cannot take actual measures.

Any info, tips or tricks for rear (and front) wheel max widht, tire size and offset clears wheelwell w/o modifications?

Forgeline says 18X10" should be safe with 295/40R18 in rear but no idea of correct offset or BS?

Thanks in advance!