does anyone know if I can use the four slot pinion, gear and new six pin brake system from a newer abu garcia ambassadeur to up grade my old ambassadeur reel?

I've never really messed around with the older c series aside from the 2500's.  What I can tell you though is that I've bought brake plates for the newer ambassadeurs and have noticed, when shopping around, that the position holders and yolks, pretty much anything involved with dis/re-engaging the pinion gear is different.  I'm not sure if the older c series yolk can hold the newer style pinion (even the 2-slot) on its c series brake plate.  Only one way to find out and that is to fit the parts.  May I suggest Walmart.  Some carry the real ambassadeurs, like the c3, that you can tinker with.  Once confirmed, return it.  Walmart hassle free return (minus waiting in line). 

 

If the pinion and main gear can work with the older 'c' brake plates, drag stack, and yolk, then I don't see why it wouldn't work.  But you also gotta realize that the spool needs to be upgraded to the current style as you can't snap on the 6 brake block clutch washer onto the older spools. 

No it won't. The end.