Originally Posted by F N CUDA

You can use the 104 servo mounts with the 103 front end no problem, you cannot use the 103 servo mounts with the 104 front end since the 104 front end needs the extra support for the rear of that assembly.

So as mentioned above you only need the 103 front end, longer tie rods, and your choice of 103 wheels and tires.
I'm curious as to why you want to change to the wider car when the narrow car has proven to be very, very competitive when it comes to racing on rubber tires since the Pit Shimizu combo is kicking serious ass now.

If you are however racing on foams I understand completely since the premount 103 tires and other similar combos will most likely destroy the combos available for the 104 sized tires and rims.