There appears to be two types of RR engines that powered the B717. BR715-A1 and BR715-C1, I'm guessing this might explain the slight difference in reversers.
As far as I am aware, the engines are the exactly the same. The A version had the low-thrust chip (18.5klb) and the C had the high-thrust chip (21klb). We used to swap chips as the seasons changed and we needed more grunt in the bush.
That IMP picture is very old; Impulse handed over it's 717s to Qantas in the early 2000s, so the components (which do look different, I agree) may have changed over time.