The 'e' or eta engines were designed with high(er) torque but low revs. A standard head and EMU will up revs and power (to an extent). I guess you will end up with a total engine replacement to get what you want. IMO the best way to go is with a whole doner car to ensure you get all matching parts. You may even end up with a loom change which can be a real PIA.
With a standard 'i' head and EMU; try headers, mild cam, 1/2" bigger exhaust and full tune up. Fix brakes and suspension/steering wear first. No point being first to the corner if you don't get round it!!
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i