Varitronic Regulator match ups

[thackers]

Please could someone tell me if a Varitronic regulator can be replaced with the B.G.M one. I'm talking the small type here, I was told ages ago that a Varitronic can't be worked with a standard 12v regulator so I was wondering if the 2 smaller and similar looking items can be interchanged ?
If I have put this in the wrong section please move it to where it belongs