The information I've been looking at is from the Briggs and Stratton Repairmans Handbook Service Manual for Out of Production Engines 1919-1981. In the Model Data on page 2 the different methods of identifying engines is explained, and obviously the method used to identify my engine would be the numeric-alpha system (as compared to the earlier all alpha system used or the later all numeric system used).
In the manual, Table No. 1 (The Complete List of Basic and Cast Iron Models) is comprised of two separate columns; the Basic Model column and the Corresponding Special Models column. This table (on page 4) lists in the Basic Model column a model 23 but in the corresponding special models column not a 23A. It does however in the corresponding special models list a 23FB, but that is not the same as 23AFB which is the model as identified on my engine label/plate. So this one thing I'm unclear about. Is the model 23A actually a basic model? If so, why is not listed as such in the table, but instead just model 23? If not, what exactly does the A in the 23A indicate/represent?
Further, in regard to the model 23FB inclusion within the Basic Model 23 Corresponding Special Models column, the way I understand it, apparently the F would mean “Flange Mounting” and the B would mean “Ball Bearing.” Is that correct? If so, the order of the lettering on my model, with the F preceding the B, is also a little confusing to me. Is there any good reason/explanation why the order of the lettering would not instead be the B preceding the F (thus the model identified as 23ABF)?

In regard to my engine type (703525), there must be some published info somewhere (which I haven't been able to find) that will interpret for me what those numbers indicate. If so, I'd very much like to know that information. So far, I have only been able to come across an Illustrated Parts List “23” (form MS-3676-9/61 replaces form MS-3676-96) which is for Model Series 23, 23B, 23BC, 23C, 23FB, 23FBC, 23FBL, 23FBP, 23FBPC, 23P, 23PC, 23R6, 23R6D Type 203010 to 203986. First of all there's no type numbers listed that even begin with 7 like mine; and secondly with no 23A included in the above model series listing does that probably indicate I have entirely the incorrect IPL for my 23A model to begin with?
Moving on, in regard to the serial number (654489), is there a interpretation/source I can find out what those numbers indicate/represent in regard to ID on my engine as well?
Any comments to help straighten me out on this business would be appreciated.