Head gasket is only $130 from IDparts, and just junk the bolts. They are C.R.A.P.
Arp studs are what you want, $370 from idparts
Valve cover gasket kit is *possibly* not needed, it doesn't hold against pressure or coolant. Just an oil seal. $40 from IDparts.
4 injector copper crush washers and O rings, $32 for all 4 ($8 each) from IDparts.
Timing belt WILL NEED TO BE REPLACED - You cannot re-use it, might as well do the full kit since you are in there, and then that will set you up for another 100k miles. $400, IDparts.
Strongly suggested:
Rockers, since you are already in there, and 90% of the labor will need to be re-done if they fail out later. $370 from IDparts.
Intake elbow kit makes the reassembly a LOT easier and cleans up the engine bay, $250 (IIRC) from Sasquatchmotorsports.com
Glow plugs - If they aren't coding out, then they aren't broke... But if you still have the ceramics from the factory... Consider the Etechno 7v metal replacements. $100 from IDparts.
Would-Be-Nice list:
Boost hoses - Samcos are great, IDparts, I think they are like $250.
GDE Tune if you don't already have one, this turns off the EGR (mostly) but it eliminates the error light if you are getting the elbow kit.
Finally... Labor - If you haven't ever done this before, it isn't a small job. I've done it and can do it in 2 solid days. For a first-timer, you are probably looking at the better part of 4 days, longer if you have weather delays or a life.
I'm still planning a trip to the NE in the near future, and nobody has confirmed yet, so the schedule is up to you at the moment. We can talk via PM, but the labor for this would be a steal compared to a shop, and I know what I'm doing on these engines. Doubtful that anyone else can honestly say that.
Better to get it fixed now, before it does any real damage to the rest of the engine when the weather gets hot. Thankfully, these engines run cold anyway, so you aren't at much risk of warping the head - But hydrolocking is a VERY real possibility. Just keep it full of water and don't drive it unless you have no other choice.