I bought a boat with a 454 magnum (89) and it has fast glass stainless risers on it. As i'm replacing the old, and possibly rusted out cast iron manifolds with aluminum GLM ones, a friend of mine told me to get rid of the risers. He claims they warp, especially after removing them and putting them on a new manifold, and leak water back into the engine. Has anyone else had or heard of this problem?

I had a friend run a set for about 10 years. Check the flange with a straight edge and feeler gauge.

I've been running my FastGlass stainless risers since the late 80's on my SBC. I modified them last year into long risers from the standard short ones. I've had no problems with mine. I don't see how just removing them and putting them on a new manifold could warp them? Unless they saw extreme heat I don't think it's possible. As mentioned check the flange for straightness and make sure good gaskets are used in the riser manifold connection. I like to run the blockoff plates and route the water thru the manifold to hose to riser.