I can't find the torque settings in my Haynes manual. I replaced the manifold gasket more than 2 years and approx. 40,000 km ago on my B20A Amazon. I torqued the nuts down by feel using a 3/8"-drive ratchet. In places where the ratchet wouldn't fit I used an open ended spanner (wrench). I stopped tightening when appreciable resistance could be felt. The gasket is still fine and does not leak.

The previous gasket blew because I had torqued the bolts down too much (I know that for sure because after the gasket had blown I tried to torque the nut down a little further and instantly sheared the stud).

I think that torqueing the nuts down too much will more likely cause the gasket to blow than torqueing them down too little. But you must also be sure that the manifold is perfectly flat. If not you will have to have it skimmed.