About as much torque as you can comfortably put on a 3/8 drive ratchet. Use cross stitch pattern, and torque all bolts reasonably equal.
But that's not the problem. Holding the end gaskets in place is. I use Weldwood (Home Depot grade) contact adhesive for some gasket aplications. For the end gaskets, rubber or cork, apply contact adhesive to the block and bottom of the gasket. Let dry until tack free, then stick together. For gasket to bottom of intake, use Hi Temp Silicone. Some use just silicone. I don't trust it to take up that much thickness and stay structurally intact under heat, vacuum, fuel, &
oil.
Another trick is valve cover and
oil pan gaskets. Contact adhesive on the side you want to stay put, wheel bearing (non-moly) grease on the side you want to seal but come loose when you want. Valve covers always come off, always seal, and never tear up the gaskets. Same for
oil pan if you want to drop it for cleaning occasionally without replacing the gasket. Works better than silicone or Permatex on water pump, and thermostat gaskets too.