You need more muscles.
Seriously though it's a bit of a bear to do by yourself. I started one bolt hand tightened on the passenger side cylinder head just so there's a good fulcrum to press the driver side down gently while installing one bolt on that side. Gets tricky trying to keep the gaskets aligned, but with enough goop, it can be done. Once you have one bolt on each side, you should be able to install the others, but might need a bit more prying to get them all started correctly.
I think my lever system consisted of two combination open/box end wrenches as there could be an issue with the rad and core support. One wrench under the intake and above the manifold with the box end towards you., then insert the open end of the second wrench into that, and pry away. Just be careful not to slip!!
Edit: As for the accessory brackets, I pretty sure I installed the generator/alternator and AC one along with the very first bolt. I *think* I did the PS bracket with the first bolt on the driver side, but cannot remember for certain.
I might have got the manifold positioned correctly, then removed and reinstalled the bolts for that bracket.
I did this job on the car that AL now has.