I did something similar last year - looks nowhere near as nice as your lovely basses, but plays well and sounds great. Pics to follow. Oh, and I spent £104 in total: body, neck, PUPs, bridge, scratchplate. I went slightly over budget, as I'd set myself a limit of £100, but still, got a new bass for a ton!
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The body was a Hondo P bass copy from the '80s (which sounded fine) but I'm more of a J player, so I took a chisel to it and 'made room' for the J pickup. There wasn't really room for the wiring for this extra PUP, so it's being run across the body for now.
The main thing was de-fretting the Yamato fingerboard - silky smooth now.