WARNING, this is just a preview to show how easy adding CalcHack to a calculator will be. It wouldn`t be of much use to add build instructions at this point of development!
Get the CalcHack PCB, you may buy the components according to the parts list from Digikey and buy the bare PCB`s separately, or just buy a preassembled and preprogrammed board (I`m planning to do a kickstarter campaign.)
In the first case you will need an SWD capable programmer to flash the boot loaders for both the main CPU and the coprocessor.
Open up your calculator, and depending on the model you might need to remove a few plastic parts to get free space for the PCB
Solder magnet wire from the CalcHack PCB to specified points on the calculator`s internal PCB (there will be instructions on how to find the pads for each supported model)
Reassemble the calculator, insert the batteries and you`re ready to go! Just create an empty TI-Basic program with your password as name and send it via the link port to start CalcHack.