#OOPS# so the manifold is pretty rough? Sorry if that's the case especially seeing as I talked you into it.
Mate go the round-port head I have a heap of crap ones here that you can try porting yourself.
AN OZITO high speed router, dremel, engraver is available from Bunnings for AU$50.00 and there are also a heap of other stone bits there for sale individually.
Get some crap heads and have a go yourself, you can have the #OOPS#ty ones I have here for free. I would lend you my Dremel tool but it's all the way up in the tropics, right smack bang on the equator where I'd rather be.
When you feel you are confident enough to enlargen the ports on both the intake and the head then go for it. Take your time and do all ports at the same time bit by bit. No point going to town on one port then not knowing how far to go on the next.
Then put together a few hundred bucks and get bigger valves installed.
Bigger round ports will pull some good horsies, and I actually think this'd be a more suitable street engine than some of the more worked beasts around.
elemental_funks B10 and round port A15