Autograss Class 1 Engine / Exhaust questions

I’ve got a Class 1 Autograss K11. It’s a 1999 1.0 litre and the rules on engine mods are pretty much that you can’t touch them. The one area you can do something is in the exhaust. You are allowed to remove the catalytic converters and replace them with a section of tubing of the same diameter as the rest of the exhaust. Whilst many people will do this to the 2nd cat under the car, I know people that don’t bother with the 1st cat on the manifold. This may perhaps be because it’s a major faff to get a piece of tube in there to the replace it, I don’t know. The question is, I think there is a lambda sensor further down the pipe from the 1st cat(?), so if I remove it and replace it with tube, will it send the ECU haywire?

Also whilst on the subject of exhausts, does anyone have any opinions on the best flowing but standard looking back boxes? I’m guessing different manufacturers of standard replacement back boxes will have different designs internally and some may flow better than others.

Finally, has anyone ever messed around with the ignition timing to make more power? In racing at my club’s track, you accelerate from 1st to 2nd and then stay there, revving the engine quite highly but not hitting the rev limiter (it can hit the limiter at some longer tracks). I was wondering if there is an ignition timing setup which I can use that makes more power at higher revs, perhaps to the detriment of power lower down? I’ve even thought about super unleaded with more advance but I don’t think that will actually make more power. Any thoughts? Maybe I just need to sort the exhaust and get it rolling roaded.
For info I’m about mid-pack in terms of performance but I’ve done nothing to the car and aside from stripping it and putting the cage and seat in and fitting knobbly tyres etc. it is as it was when it left the road. If I could just improve the power a little bit perhaps I would be more competitive with people who spend a few thousands (I’ve spent less than £800 all told).
Oh, final question – what are normal cylinder pressures on a 1.0 if I do a pressure check?
 
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