It shouldn't be that difficult to completely remove the motor and all its associated fittings, you should be left with a basic 335 head unit. Then just fit a servo, again it shouldn't be that difficult as folks on here do it all the time. A 550w servo will work, a 750w would be better.
A closeup photo of the needle/feet area would be nice, to see what feet/feed dog are fitted.
Oh, and you might be able to sell the Efka, seeing that you have a working unit.