17 and in need for power!!

I'd say tune up that slant six. But don't be too elaborate with it.
You may have many part to build an awesome 340, but I would still save up money and time for an actual swap to a V8 if I was you.
You still need to either get a V8 K member or get one of those S6 to an LA V8 adapter mount kits. You'll need to get a transmission that'll fit behind that V8. I would also upgrade to bigger torsion bars. I imagine you have fairly small ones compared to a V8 equipped one. My duster has .87 (318 equipped Duster, I now have a 360 in it) which is still on the small side. You most likely have a .83 or .85 torsion bars. (unless it was changed out before)
You can easily build a 400+ hp 340, it does not take much.
My 360 is pretty dang close to 400 hp mark and I didn't spend that much (helps that I did most of the work)
Save up even more money and you can even build a stroker for even more power if you want to.