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If anyone is in the Dallas area and is thinking of going LS but not sure I will be more than happy to take you for a ride and help you out with sorting parts and cheaper routes.
BRP has headers designed to work around the mounts they made. I don't have any but I do have some of their 3/4 length headers. You would have to call and ask them about using other headers with them, but as long as it doesn't move the engine to far forward it should be ok.You can use the factory PS pump from the LS motor. If yours is the metric box it will bolt on, if not you will need an adapter fitting.