Thanks for the comments!
Dave, yes I did use mirror lockup for this, along with the cable release, as I do for most of my multiple exposure sequences. Having the external dedicated MUP control makes it simple. The 645D mirror is very well damped but it's still large and has a lot of momentum in there. Even at the 645D's modest frame rate on a well locked-down tripod, doing AEB bursts is different than single shots handheld. I don't want to make the image blending software have to work harder than it needs to to register the separate frames.
Yamanobori, nice spring shots!

The A 120mm is pretty good to focus when lighting is adequate. I sometimes rock the focus back & forth like Dave describes and can nail it pretty reliably. I do miss Live View from my Canons, though...