Long time lurker here with a few posts.
Several years ago I picked up a Remington rolling block rifle that is obviously a rebuild of sorts. It's a 1 1/2 action that has been rebarreled to 45-70. The 27" round barrel tapers from 1" at the receiver to about .8" at muzzle. Only markings is a somewhat ragged "ballard' on top at mid barrel.
There are very faint traces of a patent date on the right side of the receiver which measures 1.14" wide. All else about the action follows the 1 1/2 criteria: half octagon top, smaller hammer spur and thumb piece.
The fore stock is a simple shotgun style. The butt plate is US marked and is identical to the one on my trapdoor carbine. Overall it is inexpensively but nicely done rebuild. 
I got it cheap at a large gun auction.

I have some concerns and would like some feed back. Reading my copy of De Haas book on single shot rifle I see no mention of the 1 1/2 RB ever being offered in 45-70. Knowing that it is an older BP action, I would never load her up with powerful loads, but is this action OK for trapdoor loads only? 10-14 gr of Unique behind a 385 gr cast RN is what I've been shooting.

John

Your are correct it is a 1 1/2 action . As you said the thinner reciever, non rebated octagon top and rotary extractor. The b block and hammer will fit into a #1 sporting frame. The shank is 7/8” I believe which is the same as a trapdoor has if I am not mistaken. So you have a stronger lock up than a trapdoor and the same barrel size. I realize Frank and others Saudi  it was only suitable for 38-55 class of cartridges and similar. Draw your own conclusions. 
    Also they are pretty scarce.