Just remember, all the modifications raise the rpm of the power curve. I've flow bench tested 250 heads several times, one stock, one modified. The modified head had bigger intake valves, narrowed head bolt bosses, and epoxy filling the floor ( same as the lump port pieces ). I was able to get better air flow from the exhaust with just cleaning up the ports, the intake flow improved due to the short turn from the port into the valve face. If I remeber right, it gained about 20% air flow at the highest valve opening. The lump's raise the floor so the air will follow the natural curve and make a decent turn into the cylinder. A stock head port floor has no curve so to speak. Removing the head bolt boss opens up the port, and yes you gain air flow, but loose velocity. The port becomes so big, at low rpm the air is hardy flowing. Race type 250 engines run in the 7000 rpm range or more,thats where the big ports really help.
My modified head was on my truck for several years, it seemed to run alright but always had a shutter or shake while climbing hills. I finally figured out the head was causing the issues after changing a lot of other parts. When working the engine at part throttle, the exhaust flowed so good that when the valve timing overlapped, the fuel mixture was pulled right through and out the exhaust creating a lean condition. It all went away with a stock head back on. The flow numbers for the intake and exhaust were equal on my modified head, when they should be around 20% less for exhaust. When I went to scrap out the head, I found 4 of the exhaust seat bad due to heat from running lean.
For sure use 307 V8 Chevy pistons, 9:1 compression will help, probalbly more then head modifications will for around town driving.
