Ideally, you'd buy the two guns out of retail stock, and make sure that they swap barrels before laying the money down.
Having confirmed that your two frames interchange, you can send one frame into H&R and have two more barrels fitted to it and switch the four barrels indiscriminately.
I've had situations with not quite identical guns where the short barrel fits on the long frame and feels good, but the long barrel won't easily latch in the short frame, so switch barrels on both guns when you test fit them.
I have five frames, three of them can take each others' barrels perfectly, the other two don't match the three, or each other.