496 ho oil in coolant
 

I have a 32 Fever with twin 496 HO'S with 2300 Whipples. 1st trip of the spring noticed oil in coolant resv starboard. I checked the closed coolant protection was below dexcool 50/50 and very possible cracked head. Oil is clean. With the understanding that oil cooler is supplied by Seawater there is no way oil cooler could contaminate closed system. I cleaned resv reinstalled and ran up to temp @ 160 and oil again contaminated the closed system in the resv. prior to my removal and disasembly of the engine is their any obvious checks I could look for. Leak down is impossible with port less than .75" apart. If I had a cracked block Wouldnt I see coolant in engine oil? Any insight or words of wisdom would certainly be appreciated.
Not looking forward to Pulling this engine again.