I have the hrt210 but I bought a 8" flat back bison chuck then drilled 6 holes through that way I need NO backing plate.
you need to buy a flat back chuck and a adapter plate OR just drill the holes through. that are on the back side saving the price of a back plate.
One thing I will reccomend DONT BUY A BISON chuck they went to ****. buy a buck chuck its well worth the money. the bison chuck is gritty although it smoothed out a tad after I lapped everything in but its still junk (cause its gritty) however it does hold run out fine.
Haas was selling bision chucks I thought(hopefully they sell a better one now). if you get a gritty chuck send it back cause you will hate it on thin parts.
Gritty meaning when you loosen or tighten it down its not smooth.