The porting never really worried me much on that gun.
There are most likely a few reasons for this.

Firstly my hearing has been badly molested by several '50s BSA rifles I've owned, which were fitted with factory muzzle brakes.
And yes, they were damn noisy things, especially on the 30-06.

Secondly, the 458 being a fairly low velocity cartridge with the 500 grainers, didn't seem to be anywhere near as bad as porting on higher velocity rifles.

Third, the rear ports on that rifles magnaporting, were not angled towards the rear. They deflected the blast straight out to the sides.
Sometimes/often the ones who cop the big blast from muzzle brakes are those standing close when the gun is fired, but it wasn't too bad in that respect either.

Ron Webb commented that it was a very early Australian Magnaport job, one of the first to be done here.

The reason I let the rifle go was that one of my clients really wanted to buy it, and I had a Joseph Lang 360 No2 NE double to use instead.

I know what you mean though, I hate muzzle brakes with a passion, but that one wasn't too bad in the noise department.