A Sohc will get plenty over 300 AND will make torque. They have a longer stroke (90mm vs 77) and the same disp. It will make more torque down low. Dont under estimate the sohc.
Also if your looking for 250whp a set of vitara pistons and forged rods will do that for less than 500 bucks. Id like to see you build the internals of a b16 for that. Straight From FJT you can get a complete rebuild kit including all the seals and belts water pump pistons, rings etc, and then rods for a total of 589. HA!

With that plus a cam some head work and an IM your ready for 350.