I have a 1986 z28 with a 350. I’m the second owner and I didn’t install any of the parts but I know from an inspection that the collector flange on the passenger side header is leaking. I have already bought the appropriate gasket but it seems like a pretty tight space to get to the 3 bolts. Does anyone have any tips or advice for getting to them and getting them unbolted so I can instal the new gasket?

 

Based on 3/8" hardware requiring 9/16" wrenches and sockets, I've gathered a few needed tools. A 1/4" drive 9/16 socket and a selection of extensions allow you to approach the fasteners at a distance. I find there's more room upstream and downstream of the flange itself to fit the smaller 1/4" drive ratchet in there. Might have used a 12" extension or longer. I also have a short 9/16" combination wrench the tucks up in there.
Same set of tools worked for short, block hugger style headers as well as mid length/full length headers. The latter was much easier to work with.

 

Just got out from under the car this morning and I found out it’s an 11/16 but and bolt but while I can get a socket on the bottom there is no room for one on the top so the bolt just spins

 

Is there room for a stubby box end wrench?

 

There is but there isn’t enough room for my hand to grab it. I was thinking about buying a but splitter but I heard for the most part they are junk

 

The nut splitter needs room too.
Maybe with the right wrench it would rotate with the nut and then itself against body or frame.
One other thought would be to hammer in a slot blade screwdriver between the nut and and the header. Maybe you can wedge it sufficiently to keep it from rotating.
Just throwing out some ideas....