An uprated front stabiliser bar will help keep the front end level on turns. If it hasn't been done, swap the rubber LCA + stabiliser, radius rod and end links for urethane. It will improve handling and feedback. It's good to know that the PO did start on making worthwhile mods like the balance shaft delete. The Weber is more vacuum sensitive than the Mikuni and requires dialing in by trial and error. It will need more initial advance but if you want to nail near optimal midrange torque and you can handle old school tuning, try this - set your plug gaps to about 0.85mm, start the engine and loosen off the distributor lock nut. Hold the throttle open to around 2,000 rpm and gently swing the distributor between advance and retard until the rpm's increase by themselves like a small spike in power and lock up the distributor, then test drive. If you get a sign of detonation, back the timing off a little. It is recommended that these engines are run on premium fuel as they are reasonably high compression from factory. You might not get any difference in power if the PO has put the time into tuning it. The jetting might not be 'spot on' for the 4G54/G54B either.

*tips for using a Weber - don't use an 'open air' filter as it'll suck in all of the hot air from the engine bay (good for throttle response, crap for torque and fuel economy). Technically the mechanical advance on the distributor needs to be modified to match the Webers' throttle curve but you can get it in the ball park by trial and error. The Weber works best as part of a package - porting and port matching, polish, headers and EGR delete/disable. A wider duration cam will finish the job (big lift can and most likely will kill power - it is not advised on Mitsubishi SOHC engines like the G52B/G54B/G63B/4G64) The Weber does it's best at open throttle so once you get it up over 3000-3500 rpm it should really come to life.

DON'T BEAT ON IT IN 5TH GEAR. Guys can destroy 5th in stock factory trim but it's not due to the gears being fragile. The gearbox housings flex which causes the shafts to wander out of alignment. Once only the outer sections of the gear teeth do all the work, it stresses them and then ping, teeth get sheared off. A reinforced cover plate will strengthen the rigidity of the gearbox. A gadget called the 'TUFFPAN' will ensure your gearbox can soak up 500 hp no sweat. It's over kill and I'm pretty sure there are factory alternatives.