there are alot of guides on t'internet showing how to use custom models in sfm, quick google should suffice?

I'm doing some "beginner" style animations and am using custom models. for some of these models, the "root transform", or atleast the point which the graph editer modifies relative to, is not in the centre. therefore, when I try to have the object roll or spin, the whole object rotates around a point at the extremity of the object, rather than the centre.

In this specific case, it is a simple ball prop, where the root transform is located on the circumfrance of the ball rather than the centre. Rotation is applied around that point, as if the ball is rotating around that point. Obviously this makes a rolling animation in its current state a bit difficult.

Is there some obvious method that i'm missing? I feel like this could be a fairly common "problem" that people solve.

I've downloaded a few maps from the garrysmod(.org) site, usual .BSP files. I've tried a couple of ways of bringing them over by copy+pasting BSP, texture, model files etc, but this appears to be futile. I've seen a few places saying that you need to decompile and recompile the map (or something along those lines); however, I wouldn't like to do this if there is some alternative.

is that my only open? to decompile and extract etc? or are there other ways?

Sorry if this is an easy/stupid question, I've only just started properly going for it in SFM