well I knew one thing different between F-5 and F-20 that take some room
- Type: afterburning turbofan
- Length: 154 in (390 cm)
- Diameter: 35 in (89 cm)
- Dry weight: 2,282 lb (1,035 kg)
that's 1m difference in size
- Type: afterburning turbojet engine
- Length: 112.5 in (286 cm)
- Diameter: 20.8 in (53 cm) inlet
- Dry weight: 684 lb (310 kg)
The big problem with your post is that OWJ is not churning out any variant of F404-GE-02 so its relevance here in this discussion is useless. It's an old turbofan which was designed in 1970s. Had revolution happened 2-3 years later we would have had our hands on it.
What we do have is a single crystal turbofan equivalent to FJ-33, called Jahesh-700.
FJ-33 => Larger version FJ-44-4A (20-21 Inches dia, 53 Inches length, dry thurst of 3600 lbf)
Jahesh-700 => Larger Version Jahesh, lets call it Jahesh-X (20-21 inches same as J85/OWJ, 50-55 inches length, dry thurst of 3600-3800, Afterburner 7500-8000 lbf).
So same dia, much less length, Jahesh's FJ-44-4A version will be almost interchangeable with OWJ J-90, but may require a redesign of air intakes like in 3-7600 Saeqeh. Its reduced length will also make much more room for advanced avionics in the future or maybe internal fuel. Future generation may look like this.
Technologies already present are underlined
-2x Jahesh-X on Kowsar airframe (more composite) will result in ~15000 lbf
-highly maneuverable (F-5E/F, F-20, F/A-18, Saeqeh family is highly maneuverable airframes)
-RCS of ~1 m2 (reduced even more with RAM, V tails of Saeqeh)
-Datalink with G-WACS network of OTHRs and AESAs like Sepeher, Qadir and Asr etc
-2 x All aspect HOBS WVR + 2-3 x ARH-BVR
-IRST IEI TIC-S-2 long-range infrared with 150 KM passive detection (in use)
-AESA like Grifo-E (Bayyenat-II is domestic ditto of Grifo-346)
That will be the machine that IRIAF/IRGC-AF can take into the unmanned era to fly along A2A UCAV's. We just need some patience.