We have a lot of inexpensive amp kits for older Fender amps. They are compatible and can be used together in lots of combinations. As an example, A Pre CBS kit, a Heat Up the Normal Channel and a Reverb modification kit can all be installed on the same amp with no problems. Also a Dual Stage Master, and a line out kit can also go on the same amp.
But - larger kits, such as the Super Texan etc. ARE NOT just collections of smaller kits. They are complete technological rebuilds of the amplifier from input to output.