with what your planning, i see 300bhp pretty easily. 300whp on the other hand may be pushin it abit.
you can get to abit above 200whp with bolt ons. intake, header, AFC, exhaust should get you there. i did 198.34whp. add in a timing adjustment to 13-14btdc, the egr block off plates, TB coolant bypass and maybe you can get another 10rwhp.
that leaves 90whp for you to achieve that goal of 300whp. So you can open up the engine, make it rev higher, flow better,cams, cam gears, get a stroker kit, overbore, higher compression, lighter rods and pistons, lighten crank. thats about all i can think of.
if you can get to 300rwhp that way more power to you, but do you really want to run 100 octane everywhere and spend over 10 grand? i mean isnt the 3.2L stroker kit like 7,000 and the 3.3L stroker like 10,200?
another thing to keep in mind, the I6 likes to give torque gains over hp gains....unless you go with a large exhaust.