Firstly, if the outer isn't damaged/rusty inside, just reuse it.
Regarding the speedo head, you could remove the 'Clock from the box' and soak it overnight in a dish of kero/oil mix. Put it in face up but keep face out of solution, probably wouldnt stain it but might effect old paint. The use an old small screw driver or similar, ground to same square as cable, carefully work it back and forth ti ll its free. Make sure it doesn't grab needle side and over wind the tiny clock spring behind needle. It's usually just dried up old grease the 'sticks' them up.
If thats succesful, give it a spin using old bit of cable in a battery drill.
Clean with brake clean and lube sparingly.
Or take it to instument place.......if you can find one nowdays.
