I recommend you contact a local relining pro. They can assist you with the sizing, choice of alloy, brand, warranty, termination cap, and installation. An 8" is huge, esp. for such efficient equipment. Also, you may want to insulate this liner to minimize condensation. Probably will want AL 29-4C alloy instead of 316Ti. Type 321 is garbage and doesn't hold up. It is better suited for jet engine nozzles.
I've used this product before. They can custom roll up to 12" diameter. 50' shouldn't be a problem for them to make, but it will be pretty exciting to install. (Think Heavy)