Uber,
Being honest, if had a '68, then wouldn't be looking at either Red9 or bj dropped spindles. :shock:
If your bus is a '68 then it should have the earlier bolt pattern on the beam and the early style chassis legs.
Would just put a split beam (stock width one) in there. Early beam bolt pattern means they bolt straight in.
Will ride lovely and, if you get the brazilian dropped spindles for it, you can bolt up your late bay discs (and adaptors). If you don't go silly low then you shouldn't need to notch the chassis on an early bus either.
Stock split beam is about 20mm narrower than the bay bj beam (loses the width of your adjusters) and the torsion tubes are closer together which gives you about an inch and a half more ground clearance.
All good really
Not expensive either, sale of your current beam should fund the split one and k&l dropped spindles are lots cheaper than the bj ones.... 8)