Gee... even this old dog learns something new.

I did a a search on google images for Bruticus (to help offer an answer), and I was seeing a lot of recent images of Gen1 Bruticus with Brawl having the tank turret at the back (it was always at the front during Gen1, with the toy photos, cartoon and comic). And now I see why... the artwork on the original boxset and the reissue box always had Brawl backwards.
I never noticed that, and thanks to the recent reissue boxset having Bruticus artwork on the front (which Gen1 Combaticons never did in Western countries), we only ever saw Bruticus as a toy photo... not the artwork with Brawl backwards.

I had a look on the tfu.info website, but even they have their toy photo with Brawl backwards.
So I guess it is an official toy-accurate version if the box-art depicts it... even if it may well just be the error of a single artist 20 years ago.

Basically, it is up to you, how you want it to look on your shelf. If you want a Toy/Comic/Cartoon-accurate appearance, refer to this picture, from this page with lots of other pics.
Oh, and point Brawl's barrel upwards, like a spiked kneecap.

Also note the other way of having Onslaughts arms. Pointing them out the back will give him a sleeker abdomen, similar to how he appears in comics and cartoons, BUT, those arms can sometimes be unstable (especially if the toy is old and loose)... so often people will have the arms by the sides so that they lock in with the legs.
Again, it can end up being a choice of the collector.