Was it the Gasoline resin conversion kit you purchased? They come from France. That's what I used. I'm in Spain at present, but from memory you unscrew the screw or screws underneath the corgi model. You then wiggle the top and bottom of the hull until the come apart. There's a knack to it that once yo get it right you can do it in seconds, but it doesn't take brute force.
Once that's done, you remove the screw which holds the turret in place and remove that. The Gasoline turret on my model needed a larger screw which I found in my tool box. It isn't perfect as when I turn the turret one way I am screwing it on tighter, whereas the other way I am unscrewing it. However, it does work and the screw is hidden inside the model. There's a photo of my one in the Chain of Command rules.
Hope that helps.
Rich