I believe 2ndGenTeg is correct regarding the intake. Your G2 intake will fit the B18C. I have two friends with C5s in their G2s and their LS intake carried over fine.
Regarding your first question, Wings West make a 90-91 lip for the front bumper. It is the Wings West RS Racing Series lip:
There is also the OEM kit:
And the much coveted but discontinued JDM Hiro lip:
