In my opinion you did everything correct for an excellant street engine. The use of a big port intake on a small port head gives you exactly what you really want which is the most low end torque you can get. A small port head will probably get you 4500 to 4800 rpm with some more carburation but at some point your going to give up low end driveability. The Nicson cast iron exhaust are really not that good. They come out of the head and make a direct 90 degree flat corner. I ran them once at El Mirage for the heck of it and lost 35 mph.
You don't say which small port head you have; if it's one of the last ones with the quenched area around the valve the addition of a 302 or "H" head will loose you compression and you will probably run out of intake air with only 2 single barrels. Good Luck
