Is there actually anything physically wrong with the old original butt? I ask because it LOOKS to me like you've got a new No1 rifle butt there. While it'll fit, after a bit of simple carpentry, it ain't right

If you do decide to fit it, there's also a thread on this forum that details the fitting and the clearances that you must maintain

to remove the pin that retains the backsight axis pin, use a drift with a smaller diameter than the pin and you should be home and dry

Fitting a new bolt and CHS-ing your rifle afterwards.......... There is a detailed thread explaining how to do this PROPERLY. Look it up and read it. Then read it again. You'll find that you probably won't get a bolt head that'll close on a .74 gauge so I'd beg, borrow or steal the .064 and .074" gauges, fit the bolt to the rifle THEN CHS it