Hello Chris, Talk to Rich Hardy VMG parts he may be able to help. I obtained a new pair of these castings from him a year ago. If my experience is any thing to go by you will look hard and long for a second hand pair. I have yet to fabricate the complete manifold. Cheers, Mike.
The bolts were to attach the steel panels to the side of the block, a poor attempt by MG to disguise the origin of the engine and resulted in overheating, hence why few survive