I'll be doing some flowbench stuff in the not too distant future with a 38mm exhaust 531 head.
I'm not convinced on the need to drill holes into the head for coolant flow as its like opening up a thermostat, but i won't know until i compare directly between Sam's motor and my one with a infra-red temp guage. Based on my 122 with two temp sensors, one at each end, the difference in that is 5* at any time.
http://www.pbase.com/towerymt/531
A decent looking ported head by towerymt, there's a few threads on tbricks covering it too. Of course without testing, you may just cause stalling.
For the size of the intake port on an na motor, i hope you change from the stock intake, but there isn't that much to do to gain a lot of flow as such on a 531 with the casting shaped for fluid flow.