3x 3/8" BSP (have two already got of a forum, need another three)
1x 1/4" BSP
1x 5/8" ID tube tee line

Final edit: Have gone through the airlines site properly, and they do have what I'm looking for.
3/8" BSP barbs in 16mm OD (near as dammit 5/8") are part number 112328
5/8" tee line is part number 111113
No sign of 1/4" BSP, but to be honest I wasn't expecting any - I can live with 1/2" fittings for this one.

http://www.airlines-pneumatics.co.uk...ctCode=S010142 is the barbs page.

hmm - that link seems to be for BSPT fittings (and nickel plated - don't know how that mixes with other metals? silver??) - they don't have BSPP beyond 13mm... (in any material...)

http://www.engineersedge.com/galvanic_capatability.htm
Copper/Nickel is about as bad as copper/brass. Even nickel/brass is rated as being OK for harsh environments. Nickel/silver is maybe getting a bit dodgy though, but again not as bad as copper/silver.

In any case, they're presumably electroplated - in which case the mass of nickel in the system will be tiny. At worst they're only going to strip the plating off the barbs (probably reacting with the barbs themselves actually).

so it's just the problem(s) of Tapered Barbs in a Parallel hole then .....

Yeah, and I suspect that one won't be too bad in practice either. Probably just needs a bit of care...

Four 5.25" bays stretch quite far, if you know how:

http://pic18.picturetrail.com/VOL932...0/32573148.jpg

This is two (slot-loading) CD devices, a floppy, a multi-media card reader, and two HDDs. And there is room left for an LCD and fanbus if you want.