Hello there-  Just a quick silly question.  I have a FC that's come off from 65mm frame.  Can I install this FC into a 75MM frame?
I know the motor post-to-motor post  is 75mm, but I don't know if the FC mount is universal or not..  thanks guys!!!

Should work. The mounting holes are likely 20mm apart and that should work on both a 65mm and 75mm frame.

common whoop boardmount is 25×25mm, that should work aslong as it isnt proprietary stuff, as example emax has some

Should work in 75 and 85mm frames.
Your only issue may be motor wire length if the motors are soldered to the board, if they’re plugged in thry might just be long enough for a 75mm.

Yah thanks, fellas. Just ordered a Meteor 75 Pro frame

Although most whoop AIO FCs share the same 25.5x25.5mm mounting hole pattern, some whoop frames (like the 75pro) have ducts that extend into the AIO bay. So an AIO may not sit down well into the frame if it has straight/wider sides or plugs that come off the sides. Those frames are better suited for AIOs that have sides which curve in slightly or are cross-shaped, otherwise you may have to shave the frame a little to get it to fit. Also take note of the location of the USB/motor plugs, they should fit through the gaps in most frames, but sometimes they don't match up well.