1-Exhaust manifolds same as corvette?
Yes, they were same as Corvette. #3880827 LH and #3880828 RH
2-Are the rear trailng arms different-boxed?
No, they were never boxed from the factory.
3-Build sheets can be found almost anywhere, but the most common place is in the back seat. Remove it and check the back side of both cushions. They've been found under the carpet, behind door panels and I've even heard of people finding them above the headliner.
4-Valve covers same as corvette?
Yes and No. This info is '66 specific and there was NO CHROME! The valve covers were painted. No Tonawanda decal on the passenger side either. They weren't used until 1967. The passenger side cover is the same, the drivers side is not. They had drippers on the underside, just as Corvette. The difference on the drivers side was in the power brake booster notch. It was about the size of a 1/2 dollar and didn't go all the way down to the flange. Take note of the spark plug wire stand-offs and their position on the cover. The stand-offs are in the same position only mirrored on the passenger side. The drivers side also has 2 clips for the temp sending wire. Here's a few pics of the drivers side cover. The one pictured doesn't have drippers.
5-Was there a date these cars would have been built before or after?
They were made during the regular 1966 production year.
I hope that helps out.