Bore spacing on a Cleveland is 4.380. On a 300 it is 4.480. So using two head sections means 4 chambers will be offset .100. Using three sections means all six chambers will be offset .050. The most correct way to do this is to use six separate chambers cut .050 offset at the bolt holes to align all the chambers.
Miles of expensive, temperamental welding and pushrod relocation is required, along with other mods. The valve arrangement is backwards meaning custom camshaft and pistons are required. Not to mention custom intake and exhaust systems. Not a modification I would recommend to a novice mechanic or the faint-of-wallet.
If you do have your heart set on fabbing a hybrid head you should start with aluminum aftermarket chambers or NASCAR 4.5 V6 heads.
Or just go buy the aluminum billet head from Ford Racing.
Another easier alternative is to split TWO stock 300 heads horizontally (think sub sandwich bun), offset to increase the port height and furnace braze them back together. I had a head like this that reportedly ran 200 plus MPH at Bonneville.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING