Re engining a work van. 5.7 vortec 2002. reman from jasper. old exhaust manifolds will not quite fit on new engine. Manifolds have gotten shorter somehow, warped? Can bolt one end on, but after starting bolts at one end holes for bolts at the other end do not line up with head; off by about 1/8". If I start at the middle I can get either end to start (barely), but once I get a bolt in one end the other end is no go.

Is this common? do these manifolds shorten up over time with heat cycles/warping? What is the fix?

Considering drilling out bolt holes in manifold to allow a little more clearance, but there isnt a ton of extra material there. create a jig to spread them, bolt them on, then remove jig? heat them up with torch to grow them a little, then bolt in place? all ideas I have feel like asking for cracked manifolds down the road. Should I buy new manifolds?

I have ran into this problem quite a few times.....what I will do is use a "rat tail" file and give the outter bolt holes an 'oblong' shape, removing the manifold material from inside the bolt holes. Basically turn the circular bolt holes into the shape of an egg. No need to file the entire bolt hole to make it bigger in diameter, just file off the offending material so your manifold bolts get a straight shot into the cylinder head.

I used to drill the holes a little larger to gain the increased clearance, but have found that the manifolds may crack (at the bolt hole). Using the file to remove a small section of the manifold material has not resulted in any cracked manifolds.

Works every time.....takes probably 15 minutes per hole.

Elongate the two end holes and start bolting from the center.