New bolt head or whole new bolt assembly?

I have a model 12vlp in 300wsm that I'm thinking about rebarreling to 243. Is the stem length of the bolt head the same on both? Will the firing pin protrusion be the same (I'm thinking this will be dictated by the length of the bolt head stem)? Or would it be easier just to buy a whole new bolt assembly with the 308 size bolt head on it? Thanks.

You'll need a standard firing pin assembly and bolt head. Everything else will swap.

Thanks. I thought I might have to change the firing pin assembly too.