The 99 Sr20de has Roller arms on the cams, different than 98 and below, SO.. will a G20 ECU work on a 99 SR20DE with Rollers??? is there any way to do it... ALSO can you swap in the 91 cam like the 98- below models can? or will going from roller to 91 cam mess it up?

The USDM SR20DE cars didn't go to roller cams until 2000, so you're good for a '91-'93 cam swap.

The '98-'99 ECU has slightly different pinouts than the '95-'97 ECU. A '95-'97 JWT ECU can be modified to work, so my guess is that a G20 ECU from the right year range ('94-'96?) could work, too.

Not my area, though - I'm a "Classic" guy. Maybe a B14 person could chime in. :)

'99 SR20 cars did not have roller rockers. You can use the G20 ECU, but you will need to move some wires around.

http://g20style.com/how_to_wire_a_95.htm

That link shows how to make the G20 ecu work.