I've just quickly thrown together a quick comparison of the relative sizes of a QRF ACAV and a Peter Pig M113 that I had in the cupboard.
The comparison is intended to be on size rather than the quality of the model, as the Peter Pig has been cleaned up and undercoated, whereas the QRF has been tipped out of the bag where it's languished for the past year of two and then clumped together with Blutack.
The QRF is also missing its headlights and the driver's hatch that I didn't blutack on (it DOES say QUICK comparison!)
So without further ado, here are the pics (hi-res if you click). I'll leave you to make your own judgements on compatibility.