What great timing you have - I'm halfway through a head gasket change on mine at the moment
Reckon on it being a two-day job just to do the basics - if you want to replace valve stem seals and lap the valves, that's going to add another half-day. I decided not to, as there weren't any signs of problems, the engine is an unknown to me and I don't have huge amounts of time.
Getting the two bolts out from under the plenum chamber (15mm socket on about a metre of extensions, miserable job from under the car as a tab on a bracket must be bent out of the way - use a screwdriver poked through the hole in the tab and reach from on top, driver's side) is the hardest part. Also the dipstick tube was a ridiculous struggle. It comes off with the manifolds, which stay on the head - the whole lot gets lifted off as one huge lump.
Most of the time is spent cleaning everything up and resurfacing the head (I used coarse valve grinding paste on a sheet of glass, because no engine reconditioners are open around here at this time of year).
I stripped and cleaned all the hydraulic tappets. My experience with the 156 taught me this is worthwhile. You rap the tappet on a concrete floor to get the piston out, then the inner part of the piston can be pulled out with pliers. Use Scotchbrite to remove any varnish, wash and reassemble so that the spring inside gives the piston a springy feel. This is contrary to advice I read in the 156 forum that states "any tappets that feel squishy should be replaced". They have a spring in them, so they SHOULD feel squishy when the oil is washed out - if not, then the inner piston is jammed and probably won't self-adjust properly, which gives tappety noises (which I had, and fixed). Also check for pitting/erosion of the top surface and replace any that are affected, since you don't want to wear the cams. The tappets will take ages to fill after the first start-up (about 20 minutes of running).
Probably more points to add but I'm writing on an iPhone and it's very late at night.
Don't forget the cam locks... I can't get those either, so I'm making do with white marks and will re-set the timing later when my set arrive from England, or when I can borrow a set on the 15th, whichever comes first!