4wd system

I took mine off the axle and made a copy with standard copper alloy brake pipe, it worked perfectly, IIRC, brakepipe is a slightly larger diameter, but the rubber hoses still push on ok. The difficult part is the Tee junctions, brake pipe Tees are expensive, so I made some up and brazed them on, I was brazing the fixing plates on anyway..

I have an idea that the old pipes are behind my toolchest, I'll have a look late and measure the diameter if they are.

You can replace the entire vacuum hose system with a better and more durable solution for under £15.
Buy 10m of 4mm id hose (I use PVC, some prefer more expensive silicon), 2x 4mm hose tees and a pack of cable ties.
Run the hoses from the vacuum solenoids around the engine bay, along the brake lines and down the brake flexis to the hubs. This is far preferable to the original convoluted and exposed hose routing.
Its a simple job that takes less than an hour.

If its the vacuum hubs themselves that are the problem (uncommon but it does happen) a working pair can be obtained cheaply and easily from anyone who has fitted manual hubs. The same goes for the vacuum solenoids.

Another simple option to get 4wd working is to permanently lock the vacuum hubs by driving a 20mm long self tapping screw through the centre of each hub. This pushes the collar into the engaged/locked position and holds them there. They then operate in the same manner as old fashioned drive flanges, or manual hubs being left in the locked position, with 2wd and 4wd being selected using the transfer case lever/buttons as normal.