I bought an 86 Fullsize Blazer and was told it had a 305 with 350 heads in it. It had a lot of problems that we've worked on and repaired but now the one thing stumping us is the exhaust manifold. It came with headers on it but the Blazer I'm putting it in has the stock manifolds, however the passenger side one does not fit. The drivers side was perfect but the passenger side manifold is just a hair to long. The bolt hole at the back end of the motor on the manifold sticks out about 1\2 an inch further than the bolt hole in the head. I've been looking online and it appears that all of the manifolds for the 305/350 are this way but it is impossible to bolt up so it would have an exhaust leak if I leave it this way. Can someone please guide me as to what year manifold this thing should actually have. We've discovered that this motor has been pieced together and was told that it is out of a '77 out of a car with truck heads on it. I am attaching a picture showing how we measured from end to end of the exhaust opening for reference and you can see how the bolt holes are all evenly spaced from the exhaust holes. I'm also attaching a pic of the same type of manifold I have and you can see how the bolt hole is further out. Any and all help would be greatly appreciated. Thank you so much.

 

The cast manifolds have a tendancy of warping. This can cause them to not line up with the bolt pattern on the heads. The exhaust bolt pattern on the 305 & 350 heads were the same so you need to try to get things spread back out so you can install the bolts. There are special tools for this job, but most people end up installing headers.