I am about to change the Head Gasket on my 420a and this winter i am looking to piece together a turbo kit for my self is there anything that I should be careful of when changing the head gasket? and is there anything i should do to the head while i have it off i was thinking about port and polishing it? Maybe putting some Cams in it? How hard is it to get the timing back to the way it should be?

get the mopar MLS headgasket, arp studs.
as for what else to put in there, how much money you want to spend?
low comp pistons , forged rods, crankscraper, cams, valve springs,etc..

getting the timing back is pretty easy, there is a write up on the main page under the mods section I believe about the headgasket.

but I could spend thousands in performance parts or just a simple headasket/timingbelt/waterpump/timing belt tensioner will be fine for low boost applications.

Mopar MLS, and honestly, the ARP head studs are worth the $100 many times over.

I think the best thing to do would be to drop some EVO 8 cams in while you have your head apart.