I know a guy sitting on several cast aluminum adapters that covert 4 inch BP to 4.5. Im not sure I like the casting, but I’m trying to find a CNC that will run small batches and have them made from billet. Those I would use.
Well I don't figure on taking it to the drag strip or the possible space the adapter will take not to mention your doubt. But it sure sounds like bolt-on easy.
