Gutting the interior is probably the most effective modification on these for more speed.
Or change the FD to a lower one, to make the best use of the power available.
Even better...lighten it AND change the FD.
This
a L and B flywheel with something like a 3.9/4.2 FD will feel like £1000 worth of mods anywhere else.
You can scrape 150 out of an N/A 8v but in cash terms its not worth it, if your handy and do it for love + some quality shed time then anything is worth it like turbo conversions etc etc
If you just want more power for the traffic light derby and instant fun then buy another car as Mk3's aint that quick without serious work.
£3k gets you plenty of choice of 200 bhp plus cars or a classic hatch which is half the weight of today's equivalent