I had a thread here about restoring some old finish mowers. One was a Befco 7' Rear Discharge that was built like a tank. Another was a Modern Manufacturing 6' Rear Discharge. As far as I can tell, it's identical to the one Northern Tool sells:
NorTrac 3-Pt. PTO Finish Mower 72in. Cutting Width | Northern Tool
Everything looks identical and I was able to get new blades from Northern. I think they make them for Northern. I can't say it was as stout as the Befco, but it seemed reasonably solid. I have a belly mower and really don't have terrain suited for a rear mount, plus I'm not sure my machine could have powered it. Sold it for $800, in OK shape, but not super great.
Not sure if that has the same chute type discharge you were mentioning, but it's nearly full width and has chains.
I can't mow fast. Too rough and too many hills and turns.