Chad,
If you handled a 12ga, try to find a 20ga to see how it handles before you order. I was going to buy a 20ga until I handled them both side by side. The 20 is heavier than the 12, and doesn't balance as well IMO. You may think otherwise. The 20 ga barrel is not 26" as H&R has it listed, it is the same length as the 12ga, 28". I ended up getting neither.
I have also heard that the rib is plastic, but don't believe it for a minute. I think it is some sort of metallic alloy, possibly alluminum.
I was at Williams Gun Sight last weekend and they had a shortened (18.5") TDC in there that had been re-threaded for choke tubes.