they say to run about 2 sizes bigger when swapping to a gen 5. if it was me, I would take the snout off and send it to Ed LaBarge because I suck at doing those types of things, but if you have the right tools and confidence you can do it right, you should be fine. as I suggested earlier, you could port the inlet of the gen 5, but if you aren't going to touch the adapter plate and throttle body, I don't know how much it will actually benefit. picking up a set of heads and porting them should net a decent amount but if it's not done right, it will hurt your performance. when I had mine ported, I also had a valve job done. I'm not aware of any bigger valves you can put in. if you do pick up a set of heads, and port them, you should also do a cam swap and get rid of those rockers. if I didn't answer any questions, it's cause i'm not sure what the answer is.
also, it says I need access to see the picture of the gen 5 you picked up.