Involved with relation to cost or manhours or what exactly?
If it's any help a B737-300 C Check is going to end up around $400K to $500K and a D Check anything $800K to a $mil at the bottom end - as a rough ballpark and not including any major nasties found, major mods., major component replacements or engine work
NB. not wishing to get complicated or create more room for misunderstanding
but the engines do not come under the airframe manufacturers maintenance schedule i.e. the C Check and are a seperate issue with a schedule of their own not necessarily running in sync. to the airframe check inputs