Just about any reference on US military arms will have reasonably good information on the M1817 with good photographs, try Reilly, Hicks and even Flayderman. Other than triggerguards there were really few variants, all, whether arsenal or contractor made, were made to the standard pattern. All M1817 Rifle locks had the rounded rear section and the inclined brass pan.
Too bad you didn't buy one at $350, that was a low price for a poor condition conversion even back then. As for Moller's book, it went through only one printing and when new (I bought my copy in '94) was $60 - more than reasonable for a book with that much accurate information, he certainly didn't get rich with those books. Current used prices on Vol. 2 are running between $425 and $625 on Abebooks, Vol. 1 is a little less but still expensive at $275 - $350. There may be reprints at some time, his work will never be surpassed, only supplemented. I understand he is ready to release Volume 3 (percussion era, post 1840) soon.