Just read your build thread (nice job by the way)
Looks like you have an early 70 there.
I have a Wagenswest 4" narrowed beam that i was thinking of changing
Splitty beams fit 68-69 bays. I made a narrowed beam for my 70 from a split beam and had to get the new end plates drilled with the later bolt pattern.
Do you want a ball joint or king & link pin beam???
Apparently all bay beams are ball joint, i've heard you can go lower on a splitty beam, would i have to change to King and Link pin + use splitty drums and spindles?