Skim the head , use flat top pistons (although I wouldn't recommend), use a thinner headgasket 0.6mm is ideal. I highly doubt you will ever get a td05 to spool like a td04 unfortunately. If your looking for more power with around the same spool as td04 then look at dual ball bearing turbo's, but they are expensive. Getting the compression ratio to around the 8.5:1 mark will yield a nice gain. No reason why you can't run 9:1 but I doubt there's enough material in the head to be able to do this without having the valves bashing the pistons at full lift.