Yeah I very much doubt you can get the throttle body assembly chromed, especially if they said they cant even do the inlet manifold, still I have my doubts, so will get a 2nd opinion about the inlet.
Yeah I used sand paper, started on 60 grit, worked my way down to 1000 grit wet and dry, then used a polishing kit. Took me over a month to do the Plenum! Its pain staking work!
Autosol is just a metal polish, you could use that to keep the shiny finish once its been polished with the proper mops.
Here is my Plenum...