Isopeura,
If the muzzle diameter is 0.750" is equates to something like a #5 or a #5.5. Personally I think it'll be a touch too heavy, but as ozhunter suggests, it'll be very very comfortable to shoot.
Friends and I have built three rifles in calibre 458AccRel (500gr at 2230fps with ease) on Ruger MkII actions ... one used a #5 weight contour (0.700" muzzle) shaped like a Ruger factory contour and hence looks exactly like a factory Ruger rifle, one used a #5.5 contour (0.750" muzzle) and extended the barrel shank at the receiver a further inch over Ruger standard, mine runs a #6 straight contour (0.750") with 1" extended shank. With a 45cal hole in the barrel my rifle at 23" weighs 4.3kg with laminated Ruger stock and Leupold 2.5x. At that weight and with a distinct muzzle heaviness it soaks up enough recoil that I haven't replaced the factory pad yet, where the other two have Limbsavers and need them!! My barrel will be docked to 21" eventually which is why I used the heavier contour. It really surprised me how some muzzle heaviness really makes a rifle hold steady and soaks up recoil as the muzzle flip is controlled. Contrast that with a #5 contoured 475" barrel I had on a 470Capstick on a Rem700 ... barely 3.8kg and ever so slightly muzzle nuetral ... I considered Magna-porting but then decided to sell the rifle as 0.475" projectiles aren't exacly plentiful in Australia and I couldn't be bothered fitting recoil reducers and leading the stock to bring the weight up.

Anyway ... reason I'm interested is on another forum there's a thread on a 423/375 wildcat ... pretty much straight walled like a miniaturised 458Lott. I'm considering building one on a Rem700 action just to see how it would go and barrel contours and their effect are what I always struggle to come to terms with! In this 423/375, I'm hoping to see something like a 400gr at 2300fps and a 450gr at 2150fps, so it's not a hard kicker ... but should be very similar ballistically to the 400 H&H.
Cheers...
Con