Drill and tap afterwards. Do NOT put bolts in the threads. They will be welded in place. The only problem with the bulkheads is drilling out the little brackets for the dual A/C vents. I use a very long self-drilling fastener, that I turn with a swivel socket mounted on my drill. Works like a charm.
61 II 109" Pickup (Restomod, 350 small block, TR4050)
66 IIA 88" Station Wagon (sold)
66 IIA 109" Pickup (Restomod, 5MGE, R380)
67 IIA 109" NADA Wagon (sold)
88, 2.5TD 110 RHD non-hicap pickup
-I used to know everything there was to know about Land Rovers; then I joined the RN Bulletin Board.