There is no need to do any soldering. Only removal of the infamous Futaba tab as the other folks already posted about. My method is to cut them off with a #11 blade then the blade can be held ninety degrees to the edge and scrapped to smooth up and trim down a bit.

Now back to that used Hitec Rx you were given. Exactly what model is it and what does it say on the label? Hitec made negative shift only, positive shift only, selectable shift and auto shift versions of most of their Rx's. If what you were given is a positive shift only Rx then it will not function with your Futaba Tx which is negative shift only.

Now first thing everyone wants to know is without the tab what happens if I plug the servos or switch harness in backwards what will happen and the answer is nothing. Just reverse the plug and you are good to go. Another trick to learn and you will never plug one in backwards on any top plug Rx if you mearly plug with the black (negative) lead facing the outside perimeter of the case. This applys to all makes of topside plug Rx's.

There were also versions of their Rxs' in the past which were for old style Airtronics plugs and in this case the Reversed polarity of the Rx's main power buss is made to match the old style Airtronics servo plugs and reversed polarity of the Airtronics switch harness. Using newer plugs in this particular Rx will instantly let out the smoke.

John