I was trying to locate my previous posts regarding the differences between SignalStat DualComms and the Dietz/Yankee 911/NAPA bars but can't locate quickly, so I'll try to be brief.
The DualComm is very similar in appearance to the other bars, but the only "interchangeable" part is the rotator. I use quotes because it gets complicated.
DOMES: I have a Dietz half bar that started life as a full size bar on a Jefferson Co. P.D. (Louisville, KY) car, pulled from the dumpster and resurrected. It functions well as a half bar because the domes have sloped sides on each end. This is the first and most important distinction. (Dietz/Yankee 911/NAPA are the same in every respect except for badging. From here on I will refer to it as a Dietz because I think Dietz sold the line to Yankee.) DualComm domes are sloped on one end and vertical on the inboard (speaker) side. They are NOT INTERCHANGEABLE.
Dietz left, SignalStat right.
SPEAKER HOUSING: The grill patterns are similar, but different. Again, NOT INTERCHANGEABLE.
EXTRUDED FRAME: The channels are different dimensions and cut at different angles: End caps on the DualComm are cut at a near 45 degree angle while the Dietz are 90 degrees. Yup, not interchangeable.
ROTATORS: Here's where it gets complicated...I also have a DualComm that needed two new rotators and in my quest to find them, I discovered SignalStat had at least 4 different versions.
-Dietz and SignalStat rotators are very similar in appearance and even share the same bolt pattern on the mounting plate, but the Dietz rotator is threaded whereas the SignalStat rotator is not.
-Dietz rotators have two different speed motors (slow/fast) and only rotated one direction. SignalStat had only one rotation speed, but in all but the earliest and latest (last) generation could be wired to counter-rotate.
-Dietz rotators have twin heat "chimneys" in the top of the can--and now it gets even more complicated. The early SignalStat cans were completely enclosed causing heat buildup and motor failure (and they weren't the most robust motors, either). Then they cast holes in the can for ventilation (didn't help the puny motors much), isolated the motor from the chassis for counter-rotation and moved the gears from top/inside of the can the the bottom/outside the can (1st-3rd generation). The last generation was an open frame holder with a bigger motor--think Dietz 211 with only 2 bulbs.
Dietz rotators
SignalStat rotators--Gen 1 on right, Gen 2-3 on left
There. That's as brief as I can get. I have extra rotators and V mirrors if you need one, but I sold the Dietz end plate to Rob.
Let me know if you need more info.