I don't know if anyone has reported on this, but here's something interesting. The last issue of Gomini magazine (June/July 2004) has an article showing a head mofification for a MCS by a shop in England called Minisprint Engine Developments (MED) in Leicester (who also does mods for the original Mini). Here's highlights of the article:

They ported and polished the head, and enlarged the exhaust ports -- and will match the exact porting to your specific exhaust manifold (i.e., header), you just tell them the header you will use. They do this so there is no step between the two elements to impede gas flow. The inlet port was not enlarged as there is not much room to work with there. They used the same valves (but will have a modded head with larger valves out later). They replaced the valve guides with their own silicon bronze tapered version, a bullet-shaped version that will impede gas flow much less. The valve seats were cut to ultimate precision -- by design on a flow bench to create a 3-angle profile to give optimum flow within the port and maximize swirl within the combustion chamber. They also paint the head afterwards with a high-gloss, heat-resistant enamel. They were amazed by how much gas flow is impeded and restricted on the standard car. They also are developing an enlarged throttle body and their own ECU remap.

Of note is that they found varying degrees of mismatch in these engines, and mentioned specifically considerable valve height differences. This means that valve spring tensions can vary quite a bit. That's important if you want an engine to run as smoothly as possible, as it means that each cylinder can be burning different amounts of fuel and air mixture. To solve this problem, they check the valves for height, and if they find variation, they trim the seats within three-thousandths of an inch.

This was a good article on head work!