The F-5 is honestly my favorite aircraft in DCS and I spend far more time in it then the F-18 and F-14 combined. You're at a constant disadvantage but the moment you gain even a small advantage you can exploit it to lethal effect. I actually shot down three F-18s over on PG BF the other day using the Tiger for the loss of one F-5 to a SAM site while doing ground attack. I'd pay quite a bit for a new version of the F-5 with all weather capabilities, an upgraded radar, etc. Could also do the Norwegian F-5A's with the ability to launch Penguin anti-ship missiles (passive IR guidance), AGM-12 Bullpup missiles, and I think it could also equip SEAD missiles. Throw in the Aim-9L which was the first all aspect Sidewinder and it'd make for a fantastic fighter-bomber. It would also give us the A variant of the F-5 which would be great for Vietnam servers.
As Norway upgraded their F-5's they added ina active jamming pod. There's also this for if they overhauled the cockpit and it'd allow the Penguin missile.
"A big step forward was the installation, under an USD 20m programme awarded in February 1991, of further new avionics equipment by Sierra Technologies Inc to replicate the F-16 cockpit in use in Norway, including an GEC-Marconi Head-Up Display, GPS navigation system, a colour video data system and HOTAS controls, Litton LN-93 lasser-inrtial navigation system and 1553 databus; the program (called Program for Avionics and Weapon Systems improventes (TIGER-PAWS), involved 7 Northrop F-5A and 8 F-5B(G); started February 1991."
Got a lot of the info from here. http://www.the-northrop-f-5-enthusiast-page.info/AirForces/NorwayAF.html