That's why you take it to a pro. Dont want some tard making your manifold into tissue paper.And air temps through manifold are now cooler And has less resistance travelling through. Despite loosing material I would say its prob a little safer, If not the same as stock. As long as too much material isn't taken out.
Regarding external gate that I think is a fair call. Hanging weight off a thinner material may not be a great idea.
Only internally gated bottom mount manifolds I found were 1800. So this was the cheaper option for me. Pretty happy all round!