got a 12bolt o type rear end order chevy 10 bolt gears for it but cant get the the ring gear to bolt up looks like everything should bolt up but wont

 

It won't bolt up because they are completely different rear axles. You might as well try installing Ford gears. Sell the Chevy gears and get the correct gears for a Type O axle.

 

YEP... That carrier in the 'O' type may look like a 8.5 but it is NOT. The bolt pattern is slightly smaller bolt circle and the inner ring gear diameter is also larger. The pinion is another difference. The 12 bolt 'O' type is 27 spline and is shorter than the 8.5 30 spline pinion. JUST WILL NOT HAPPEN....with out some serious machining...lol.

What ratio were you going for?