So do it then...one should have fun...
this is how I would do it:
1) Find the largest highest quality St. Louis Cardinals unifom image from the net or scan one in and save it as a jpg or tiff.
2) Find or take a high quality image of your friends face (making sure it lines up well with your uniform image, ie straight at camera). Try to use similar lighting as the uniform pic.
3) Cut out the uniform from the background if there is one.
4) Place or paste your friends image into your uniform pic and convert it to a smart layer.
5) click into the smart layer of your friend and remove everything but his face, and save.
6) transform and scale your friends face smart layer so it fits onto the unifrom as the head.
If you need to print this make sure you are working at 150 dpi for poster size image, or 72dpi for "life size" cardboard cut-outs. (minimums)
If you cannot fint a hires image for the uniform dont worry, just convert it to a smart image and set you canvas to 300 dpi (with the correct print size, eg 250cm x 1800cm) and scale it up. The face image will be large since you can take a pic or scan one, meaning the face will print clearly.
Good luck and let me know any questions.
The trick with this is shadows. Try to get the same angle of sun or light showing on both faces. Otherwise your eye will see it as phony.