You will indeed need to split the cases, I'd replace everything, main bearings and a crank rebuild, others have gambled and got away with flushing the bearings and got lucky, I did not, even 1 little piece missed can destroy everything, including any new top end parts.
That head looks like it's been at least milled before, but not evenly, and possibly the combustion chamber and squish band reworked.
I'd send that off (and the crank & cylinder) for a refresh to kenoconnorracing.com
do it right the first time and not cry twice.