Fitting a new micro to an old PCB

There is a circuit driving two steppers with a micro plus a gate array.

The pins used to activate the functions I need, belong to both. I will replace them with just a micro programed by me.

I do not want to do any "surgery" in the circuit other than desoldering them and auxiliary ICs not needed..

My doubt is what could be the best way to fit the micro to the board. Just in case you ask, no way to solder it in the place left free by the other two chips.

Ideas anyone?

I would use a 2nd (daughter) board for the micro controller and jumper it to the old PCB.

Perhaps some clear pics of the controller PCB (and some pointers as to what we are looking at - highlights on the images and such) would help us brainstorm...?