I have the opportunity to make plaster casts from a dissection...

As your instincts suggest, follow the casting protocol as you would do in a live subject. Prior to applying the plaster, you should ensure that all structures have been carefully prosected and oriented per your wishes, and remove any excess tissue and fascia. You might also want to apply some lubricating material to facilate removal of the mold/cast without damaging underlying structures.

If you are really interested, and wish to go beyond casting, I strongly recommend plastination. This technique permeates the specimen with silicone or silicone-like material. The specimen can then be used for demonstrations, etc., without the use of gloves.