It is not impossible to rework a beater No. 4 into a moa rifle. Might be a bit of an uphill struggle though, and not an inexpensive one either.
Rebarrelling a No. 4 is quite straightforeward, although the original can be in pretty tight. If the barrel is a scrapper, cut a relief groove around the barrel shank to release some of the torque. You will need a barrel vise, an action wrench and gauges, and likely a reamer to fit the new one. If the chamber is finished, headspace can be set by using the correct length of bolthead. Do you have a new barrel lined up?
No. 4s were rebarrelled to 7.62x51. The Cdn. target shooting conversions were intended to be used as single shots. The Brit. L42 and Sterling conversons were repeaters, used their own proprietary magazines, which can sometimes be found, but will not be cheap.
If you want to take on a rebuilding project, why not? But keep in mind that unless you can source reasonably priced parts, and do the work yourself, you will have a lot more money tied up in the rifle than you could sell it for.