The ornamental design for a "main support assembly", as shown on Page 1 FIG. 1 and as described.
To offer a standard support assembly made of Acrylic or wood, for electric guitars which will enable a guitarist to custom design his/her acrylic body and change out the guitar body whenever desired not affecting the sound characteristics.
FIG. 1 Details the main support assembly which lists dimensional information for extrusion; and,
FIG. 2 Shows an Acrylic V-style body mounted to the main support assembly.