Nothing specific comes to mind as a source, but check the adverts in one of the classic car or kit-car magazines (in the UK at least).
I'll venture to suggest such magazines are worth an occasional look, as there is some overlap with the Land Rover world. Especially if you have a V8.
(I run an old Ford Sierra, and since the engine in those is widely used in kit cars there can be useful articles on that.)
For those holes in the bulkhead, maybe sticky-backed plastic?