[Mike Taylor 3601]

188's like came on GenV 502 if so use them.From my experience they are better than 990's.The ones I've worked with did better than typical 990 I've done them port matched&bowl blened to max ported and numbers on flow bench both ways were better than 990's low lift all the way through high lifts were better on 188's than 990's.
Only problem I've seen is exhaust guides crack and leak water into valve guide which
new valve guides fix that If you are having guides replaced make sure person doing it knows exhaust guides have to be removed on GenV heads by driving them out towards combustion chamber that is from valve spring side down towards combustion chamber
the older Mark IV heads exhaust guides have to be removed the opposite direction.The exhaust guides have steps on them is why they have to be removed a certain direction or it will ruin the head. S.I. valves have Gen V bronze exhaust guides only source I found.
Mike Taylor 3601
You have to use certain head gasket if use on Mark IV block I can't remember fel pro part# without looking it up.