Dave is right about the bolt circle, 8 on 78mm. You'll have to use a Porsche flywheel and modify it. I actually made two adapter plates. I used the stock 200mm Porsche flywheel since I already had it. Ideally, I'd like to get the 228mm flywheel as it's an inch larger. But that's in the future. Take a look at how I did mine.
PS-You should use a high torque starter as well. The Northstar starter will not work!
Another thing to remember, the length of the flywheel bolts. Make double sure they don't bottom out inside the Northstar crankshaft. If so, the engine won't turn over and damage to the bearings may occur. Mine protrude out the back of the adapter by .530"
Stock flywheel. You'll have to remove the hub on the back side.
Remove material up to the bevelled edge. Inner diameter is now 3.108"
Adapter started out as a 6" by 1.5" solid steel stock. Turned in a lathe and machined in a mill.
As you can clearly see, the stock Porsche pattern is gone. The six outer bolts hold the adapter to the flywheel and the eight bolts hold it all to the Northstar.
[This message has been edited by Lunatic (edited 12-21-2014).]