People generally upgrade the tyres to 165/70R12. Most common are Dunlop SP Sport 490 with white lettering.

Many parts are interchangeable with Mehran. Steering wheel and dashboard of Mehran will fit easily if yours is broken. Brake pads, calipers and brake shoes, drums are same as Mehran, so is master cylinder. Rear axle is different.
Many people also upgrade the headlights to crystal lights and tail-lights to LED lights. Some customized front grilles also used to be available even though they never came into mainstream fashion.

Engine upgrades: Despite obsolete API SG engine oil rating, the engine performs fine with newer API SJ or even API SN semi-synthetic 10W-30 oils. The distributor coil can be changed with newer high-voltage versions. The breaker-point distributor itself can be replaced by CDI distributor resulting in amazing fuel economy improvement specially on CNG and lower idle fuel consumption. The alternator came with an old system which had a cut-out box placed just under the wiper sill, thi system can also be upgraded to more compact modern alternator systems. Cold-air intake can be installed in place of stock intake.
Theoretically the engine can be upgraded with the EFI ystem of Euro-II Mehran (2012+), but yet not seen any example of it.

People have managed to upgrade the A/c compressor with newer, low drag systems. Some people go for sound-deadening/noise insulation.

Mehran did have some benefits: both side mirrors, more headroom inside, higher seating position, the tailgate opened completely (in FX only the glass opened), side indicator was shifted to behind the wheel arch, it was better because this way lesser probability of it getting hit by motorcyclists.

It was a fully featured car, the A/c model had defogger as well meaning full-feature HVAC system. The beige interior helped the A/c’s performance too. The non-A/c model still had the A/c controls on the dashboard, one of the interesting things was that it had a functional heater, meaning the pipes from the radiator and heater core etc. were all present even in the Standard model. This made the car very comfortable in the freezing winters witnessed in most part of the country. This can be seen in the Bukhari Motors ad above.
The rear window came with a de-icing coil (defrost function). Sadly defrost was missing in the later models introduced by PS such as Mehran.

It came factory-fitted with radial tyres as standard! This can also be seen in the Bukhari Motors ad above. At that time radial tyres were far more expensive than bias-ply tyres, so you can see the lengths to which Suzuki went to provide its car with up-to-date technologies! The tyre size was 145/70R12, wider size than some other larger cars which had 4.50-12 or 5.00-12 non-radial tyres such as ’76 Corolla.

Some of the elements were really regal such as to open the engine room, there was a button on the hood with Suzuki emblem. This can be seen in the photos above. It even had those rubber strips on the doors and fenders with capital Suzuki and FX written in white letters.

One of the factors was that to save costs, the left-side wing mirror was not factory-fitted (you can see this in the photos above), if you needed it, it was easily available in the market as an “aftermarket upgrade”. The car was small enough to have exactly zero blind spots so most drivers never needed that side mirror anyway. However this doesn’t mean that Suzuki skimped on safety. 3-point front seat belts were standard! I even remember in one training session by NH&MP the instructor emphasized on the importance of seat belt by giving this very example that to cut costs PS removed the side mirror but did not remove the seat belt. Also from POV of safety & comfort, the front seats came with headrests as standard, a feature that was missing in ’80 & ’82 Corolla and just recently introduced in ’84 Corolla at that time. So this is one of the other features where FX was competitive with other, even much expensive and altogether higher category cars of its time.

thanks for pointing out