Big cam stock heads cam timing

Like the title says I am installing the GM847 and 1.6rr's. I am moving to germany shortly and just don't have the time for the heads to get sent off and ported. But my Q is should I advance the cam to bring the power down in rpms to match the stock heads better or just leave it straight up. Any info is appreciated, and I know I need heads. Also on the stock bottom end with Mr. Gasket .026 HG.

Btw which heads would fit my combo best? I was thinking CNC LT4 cleaned up by lloyd or AI

The cam comes with 4 * advance already, that should work fine.

Bret

Thank you Bret

Would you agree that the 847 is the same as Crane's Part Number: 109841 Grind Number: HR-296-2S-12 IG http://www.cranecams.com/?show=browseParts&lvl=2&prt=5&Vehicle_Type=Auto&Cylinders=8&Engine_Make=CHEVROLET&Year=1995&Engine_Size=305-350%20C.I.&partNumber=109841&partType=camshaft ???

If so, then it has 5° advance ground into it.