I checked the Morrison site and could not find any info on the A,B,C etc. designations.    For those of you who know, what would be my options for building a 56'' or 58''  Cheyenne.. thanks

Go to the site and click on "other info" and then click on riser chart.It has all the info on combinations.

Better yet call Bob, he will be more than glad to assist you.

thanks JRY, not sure how I missed that.