Not sure what brand Agri-fab used, but they sound like what you are talking about.
I have one with an 8 hp Tech. that kinda quit, ( what Tech. didnt quit!! lol!), anyway its out here in the junkpile out back in the weeds.
Years back I had a unit that was on the back of my 147 IH cadet mower. The motor on it was a 5 hp B&S and the exhaust on it was turned straight up with an elbow in the block and a 8" pipe in the elbow.
You could do the heat shield thingy and if you can get it thick enough it should guard the plastic.
The new motor could possibly run a bit cooler than the old Techs did.
You might have to rest it often during use to let things cool down a bit but at least you could get your leaves picked up.
All of my fans and outer stuff was thick tin.
