better inlet - Doubt it will help at all.

exhaust manifold - Also doubt it will help at all.

workig more on the head - This will help although you would need to be producing big power to benefit IMO.

bigger valves - Same as above.

other cam - Same as above.

Look at changing the turbo for something bigger. I recon that T3 will be struggling on that engine.

The other issue is the fact that the stroke is very long which won't let it rev very well.