If he's a really big fan of Cliff Burton:
If you look at what Cliff had (according to the items in that link above) and extrapolate a little ... it ticks a lot of different types of FX boxes:
An Alembic Bass, so an Alembic Preamp could be a good'n'
Ibanez TS-9 — lots of options and lots of mods for making it more bass friendly
Morley Fuzz Wah (see below)
Morley Boost Wah (also below)
Boss CS-2 Compression Sustainer — Get a SheepyLove Squishy from our very own Szukalski
MXR 145 Limiter — if you look at the reviews, this thing is a "hidden gem", but better compressor than limiter, but buildable!
Ibanez HD1500 Harmonics/Delay Rack Mount — Ibanez EM5 Soundtank Delay PCB is available at Aion
Boss DM-2 Delay — Madbean Aquaboy
MXR M134 Stereo Chorus — Not the M134, but the
PPCB Caesar is good to go in the bass-chorus line.
Wah/Filter
Electro-Harmonix EH-4250 BASS BALLS — Yeah, funky metal. PCBs available for this with lots of fun mods, check out Mark Hammer's version!
Morley Power Wah Boost — A TWOFER! 1) Boost portion only, 2) a Cocked Wah pedal
Morley Power Wah Fuzz — 1) Fuzz 2) Cocked-wah/autowah
AMPS > PREAMPS
Peavey Mark IV Series 400 Bass Amp — Have schematic, so this one's "doable" — might be a layout floating out there already.
Randall RBA 500 — Nothing available that I know of, so need a schematic etc...
Sunn Beta — SCORE! Several options to choose from for this one. Various PCBs vero and perf are available.
Mesa Boogie D-180 200 Watt Tube Bass Amp — This would be a killer Pre, but... maybe Bassify some of the Mesa guitar-pedals already cloned?
Mesa Boogie 4x12 — Cab sim
Well that was fun.
I don't know how accurate Equipboard is, but the Burton-Lore is aplenty on TalkBass.