Polished parts help flow more. Polish everything that doesnt have a rough finish. Rounding the con-rod helps flow as well as lightens the con-rod allowing more rpm and im sure power.

You can then polish the inside of the crank...where the fuel gets sucked in.

Polish the outside of the sleeve. Clean up any ports or if you can polish them to where they are exagerated even more. This can be tricky.

Then check out the exhaust port. Judging my d3r I doubt there will be anything to improve as my sts motor has the best looking exhaust port Ive ever seen.

The rest becomes tricky work and effects timing and other things. Otherwise the stuff I just listed is good to play around with and see what comes of things.

If the motor is used this will also help clean away old residue and will help refresh and further extract power from your motor.