[Savage GT]

Another eBay purchase, to go with the MSC Metro 6R4.

Still to address - the body sides slightly bowed along their length.

I think they all have that sir !
I fixed mine by screwing the chassis in tight, rubber bands around each end of the centre section with thin card in between, and gently heating with a hot air gun.
Let it cool for a while, removed the rubber bands, the sides sprung out just enough to leave a nice gap for body rock, but perfectly straight
If yours has the universal MSC chassis, you may need a suitable sized block of wood/plastic (mine had the Scaleauto chassis).