These should help you rudeboy
Auxiliary Belt: Removal And Refitting - Alfa Romeo 145 - 146 Forum
And as for cambelts these 8 videos are excellent but in German, Once you read what Armoore says they will make sense!
With TDC set using dial gauge (preferable to marks) on cylinder 1 and cam locking blocks in place (ensure they are for your engine, there's a slight difference between 1.6 and the others) belt goes on in this order:-
exhaust cam pulley,
automatic tensioner, coolant pump pulley.
Tension belt to the maximum, tighten automatic tensioner nut.
Loosen and tighten the screws on the intake pulley followed by the one on the exhaust pulley, there are holding tools for this and mind the cam sensor behind the exhaust pulley as it is easily damaged if not careful.
Remove locks and turn crankshaft twice in the direction of rotation until TDC achieved on cylinder 1 again, replace cam locks as a check, release nut on automatic tensioner and adjust tension so that pointer is now in the centre of the hole. Tighten nut to 21 to 26 Nm. Exhaust pulley nut is 100 to 124 Nm, intake pulley bolts are 12 Nm. Spark plugs 25 to 35 Nm large, 10 to 12 Nm small. Camshaft bearing in oil 13 to 16 Nm. Cam belt idler to 21 to 26 Nm. Balance belt tensioner nut 12 Nm."
YouTube - Replacing the timing belt on an Alfa TwinSpark 16v (1/8)
As for head gasket im sure there will be others who can help! Sorry! but! thankfully its a job i have not had the pleasure
Good Luck fella.
PS: Do NOT!!! attempt these jobs without the correct tools as Escy has already advised.