The chamber does require unshrouding just the same as a 18cc head or a 22cc head. The area that is shrouded is similar on all of them because of the bore, no sense enlarging it further or you have no headgasket support. I use a ball end mill on a rotary table to unshroud as in the first picture. Also all heads I flow test are on a 70mm bore adapter. My bench has sliding sleeves so I can fit the correct bore adapter to match the engine bore. I am building a 72mm tillotson motor and that allows me an additional .040 for widening the chamber. You do need to open up the dowel holes on the clone heads for use on the non hemi predator. For this build buying a ported head and a mikuni flatslide I think is poor bang for the buck (185 + 95) The best bet is keep the chikuni get the seat and throat cut correctly for a 28 or 28.5 intake and call it a day. Also the 14cc heads I do are close to 16cc if they are not milled. One last thing is if you go get a larger intake you can mount the head valve seats up and use strips of emery cloth about 5/16ths to 3/8 wide thru the port an out the valve hole and go in a shoeshine motion to put a radius on the short side brings up low to midlift flow a lot. Also the MCSA of these heads is the interface of the runner to the bowl. Leave runner opening alone but you can widen it just a bit at the last 3/8ths of an inch before the valve bowl and the entry to the bowl. Then you can raise the root and streamline around the guide a bit. Do not get carried away. The runner taper is good for hi lift velocity but when you open it up a little just before the bowl it slows down the air a bit and makes it a bit easier to navigate around the short side.
the old 212's or I should say the ones that first came with the small valves had the small dowel pin locations has the clones and honda's . then they had to change the design? early 212's are gen1"s and newers are gen3's?
even with the radius cut in the head that's still not bad for a stock unmilled head that's going on a 2.835 bore. still put you in the 12.1 comp.
for bryan he wouldn't have to mill much to keep is compression up on a 212 bore. i am assuming ole you are running narrow stem ss valves.
when i was cutting a radius my tecumseh 356 build i use the boring bar setup and fab a tool holding with a piece of high speed tooling with a radius cut into it. it work good. now that i got a rotary table i will try it with a ball end mill.
explain little more on the flatside
carb issue. are you saying he should stay with a 22mm round or can he still improve with maybe a 24mm round?