Top men in the ways of science have told me the pendulum theory is bunk. An ancient theory that went the way of that comforting Earth centered universe we held for so long. Proven wrong by 20th Century aerodynamics the age of the tractors was over, only useful for LES applications and silly oddrocs.
The Apogee tech paper on 2 fined rockets with the fins and motors in back (Where they should be! I sure do love my traditional 34FNC rockets!) Says that sort of design won't work.
As for canted motors you can get by with a little sin, just needing them to light roughly at the same time. Lord willing they will burn roughly the same amount of time with roughly the same amount of thrust on each side. Pop-pop on the ejection timng is roughly the norm as is the more than adequate power of the ejection charge.
Now you add sin with less than ideal launch conditions. You add sin by not having a nice thick and long rod or rail or any fault in launch system or igniters. You add a little sin going all two dimensional. Keeping away from too much sin is hard to do.
Do not underestimate the power of the D motors ejection charge. In such a small area and venting sideways you need super strength for an instant, which may mean stamped steel construction like a cheap, late model Chicom AK. Lord willing you will not get a motor (s) with a shotgun ejection charge.
Would plugged motors with electronic ejection, maybe even CO2, be less sinful than a potential bomb of 2 side vented D12's?
Well enough blather already, don't want to upset the real rocket scientists.