All revvy parts fit all revvy shells regardless of age or model. Mix n' match
Early (Viewloader) revvy shells were tough, kinda soft feeling. Came with opaque, tupperware-esque lids. Indestructible.
Later (JT) revvy shells were harder, much more brittle plastic, often translucent. Came with clear, very fragile lids.
New JT revvys use a shell material very similar to the originals but still have the fragile clear plastic lids.
9 volt: Single 9v and an eye in the feedneck. Fed approx 9bps.
12 volt: Dual 9v and an eye in the feedneck. Fed approx 12bps.
xboard: Dual 9v with a sound sensor. Fed approx 12bps, but more consistent due to faster response of sensor.
All revvys used the same motor?
Early revvys used a rigid two prong paddle. Later ones used a flexible four prong model which fed a bit faster. Six prong aftermarket paddles were available that fed even better. The new JT Revvys use a spring loaded four prong model which supposedly helps keep the thing from jamming.
Some errors here:
Not all shells are interchangeable. they messed with the shape when BE took over. generally soft side cant mix with hard. but even some of the hards dont mix. same for lids, I have come across at least 3 different sized lids.
X-boards were the "fix" for the crap boards they put in when they tried to do clear sides. the eyes were affected by sun light so they added a delay to the boards(run like crap). but they are still eye activated. sound boards were never X-boards. sound boards are from empire and they used the same sides as VL and you could put eyes in them, but they got sued by BE for the shape and made their own sides.
although the motors are all the same there is a batch from the Eagle days that run slow and are very loud.