DJH model building

[one man and his dog]

I'm building my first white metal loco kit and doing it very slowly and carefully. It's a DJH 4-4-4 Tank locomotive, their number K26. I've got as far as joining the two chassis side plates together but I haven't soldered anything yet. What I have discovered is that the side plates are too close together to allow the motor and gearbox to be installed between them. I see three alternatives:
1. File off the rivet heads on the gearbox. Seems a bit scary to me, those rivet heads are presumably there for a reason.
2. File away some of the chassis metal. Again, scary because it seems a lot of work and would have to be done carefully and would weaken the resultant model.
3. Loosen off the chassis side plates, insert the gearbox, and retighten. Might end up with problems of lack of fit later if I do that.

Any advice gratefully received.

[Walkingthedog]

Is the motor and gearboxthat came with the kit?

[aislabyjim]

Have you tried contacting DJH and asking for guidance?

[one man and his dog]

It is the motor and gearbox that came with the kit.

I thought of contacting the manufacturer but I've pestered him twice all ready due to inconsistencies in the paperwork. If someone here knows the answer it will reduce the risk of the manufacturer getting fed up with me. I know the only stupid question is the one you don't ask, but I don't want to try his patience.

[Brian]

No! Contact the manufacturer. They are the ones responsible for the kit and items supplied by them.

[one man and his dog]

Yes I'm aware of that thanks Brian but I'm also aware that I'm dealing with human beings and I choose to try and keep on the right side of people.

[Walkingthedog]

Surely you can converse with the guy without causing offence.

[yelrow]

If he is that touchy, i would be concerned, about the product.

[yelrow]

Having looked them up, product seems excellent.

[Walkingthedog]

I’ve often thought about making one but never plucked up the courage. Not sure I could do one justice.