Has anyone posted step-by-step instructions (with photos) of the installation of the forward assist, ejection port dust cover and A2 rear sight assembly?

A flat top upper is very very easy, the forward assist and dust cover will give you no trouble, sorry I don't know of any pictures.  The only thing you may have trouble with is the A2 sight, I don't have any pictures for you sorry but the way I learned how to put it together was just to take one apart.  Buying a completely stripped upper won't save you that much money anyway, many place sell them with those small parts already installed.

Perhaps this will give you a little help.
http://www.fulton-armory.com/AR-15Diagram.htm

www.ar15.com/forums/topic.html?b=3&f=123&t=384314
this is a previous post that helped me assemble my A2 sight.  This should help.

www.midwayusa.com/midwayusa/StaticPages/pdf/Instructions/AR-15%20Varmint%20Rifle%20Instructions.pdf
just found this link that midway has for assebly of just about every part of an AR-15

let me know if this helps