Or another way of looking at it is the same theory behind using non equal length headers- they will tend to lower- but BROADEN- the powerband. Same thing w/ports that are not exactly the same. And w/production iron heads, there's a LOT of room for improvement, regardless if the ports are identical or not.
But w/novices I will always recommend have the guides done, and an accurate 3-angle valve job, and back cut the valves if they have the ability or a few extra dollars in the budget. Then at home stick to the low-hanging fruit: do the bowls, clean the flash and port match the intake (NOT gasket match!) and match the headers and gaskets to the exhaust ports. Leave the short side alone. Do not reshape anything. Leave the valve size stock 1.94" x 1.5".
Otherwise, spend the money on a set of aftermarket heads.