I recommend you hire a professional structural engineer in your area.  We cannot give you an answer to "will it work" questions.  That is not only a violation of ethics and professional conduct but is not the purpose of this website.

agree with UcfSE.  there is a statement in the code regarding the use of wood to support brick.  basically, don't.  A professinal engineer needs to review the conditions and determine if what you want to do is affected by the code provisions.

The problem with wood supporting masonry has to do (in part) with the tendency of wood materials to dry and shrink and thereby causing "settlement" of a part of the masonry. The IRC allows wood to support masonry provided that all of the masonry that is supported on wood is isolated from the masonry that is supported on other masonry or steel.
It sounds like the chimney is only being "saved" for the portion above the ceiling. It may be that only flashing isues are affected by this choice of materials. I'm curious about why PT materials are used. Perhaps because of some contact with masonry concerns.  
Regarding the question of "will this work" it is important to understnad what is meant by the expression. There is the consideration that I have identified and the consideration of the structural capacity of the support components. In the latter case, I agree, it is best to have this reviewed by a professional. Vertical loads are one consideration. Lateral stability of the (remaining) chimney and the overall effect of this modification on the building are other considerations. I would expect that a qualified engineer should examine the conditions as a way to identify any and all concerns.

UcfSE and archeng59, I trust that this reply is not out of place.

From quick overview, having triple 12" joist seemed to be an over kill but I'm not clear on the situation. Also, you said, "1/2" X 3" X 4" lintels" and I can only assume you plan on using L 3 X 4 X 1/2. Lintels are used to support the structure above the openings such as doors and windows. You application for the angles sounds like more of the bracing than anything else.

Therefore, I agreed with others by recommending you retain a service from a licensed Profession Engineer to properly secure the structure.