You have done the easy mods, Phil, like Rich says you are now looking at the internals like head work, cam etc.
I think our friend Beans has done quite a lot of work to a standard 2L engine in one of his cars, which he has posted about before. From memory I think this was good for about 130bhp.
It's the law of diminishing returns though - more & more work will cost £££ but you will only gain a modest power increase. If you really want a lot more performance you might be better off looking at a Sprint conversion - relatively simple (compared to a V8 conversion) if you can find a decent 16V engine, & offers more scope for tuning in future.
Before you go for more power, have you uprated the brakes & suspension?
Tony
<font size="1">1981 2L FHC Cavalry Blue - very original & not rusty!
1980 3.5L V8 DHC Regency Red - on the road again.</font id="size1">