While BBC experts will tell you the only thing in common between the Mk. II and Mk. IV is the orange paint and the bore spacing, to the naked eye shrunken to 1/25th its original size - they look quite similar.

The 1966 annual kit / '66 mod stocker exhaust manifolds and cowl induction air cleaner are straight from the '63 Daytona playbook, very helpful if you are building on of the '63 GN cars.

I don't recall further use of that insert, tho.