confused

I am torquing the head up on my 8v after replacing my head gasket but...
I read that it needs to be done in stages, in a specail order, 40n than 60n than a full half turn (180degrees)
I have done the 40n, and the 60n, which was the max settin on my wrench! But i only turned each bolt 1/4 of a turn (90 degrees) because that was as far as thay would go!
My question is, should i use (or need to use) a exstention bar and turn the bolts to 180 degrees ( an other 1/4 turn)
I know i should follow the manual but it seems like ALOT of force to me?

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HELP any one?
