How to breadboard a Sainsmart 3.2" TFT LCD to a Mega2650?

I haven't used that particular LCD, but there appears to be a comprehensive library supporting it (and many other LCD driver chips) at: Electronics - Henning Karlsen

Shields are stackable so you just put the display on the top of the stack - or you can breadboard to start with.

As regards pin-out the library lets you choose whatever pin out you like for the control lines, but if using parallel mode (8 or 16 bit) there are fixed pin assignments documented in the download. You could try asking seller for the pinout of module, or see if its marked on the actual device.

Just be careful to check the requirements for supply voltage and IO voltage - the datasheets for the SSD1289 and ADS7843 will be your primary reference material!

I have used other LCD modules from eBay and its usual to have to do a little detective work to hook it all up - worth checking on the internet if anyone else has working things out for you and documented it.