howdy
To the best of my knowledge everything on the guns are the same except the barrel and recoil spring. They even made some MKVII in 451, it had a narrowed slide so I wouldn't think that it would stress out any other parts of the gun. I have built two .451s one Combatmaster and one Custom job w/ a Detonics seriesII slide and a Caspian frame. I used Storm lake barrels before the went belly up. Any good 45 barrel can be rechambered to .451 fairly easy. I think I have the reaming specs somewhere. The brass is still being made in small lots and will run you about 40 a hundred, if you want original Detonics brass who knows how much it will cost. The new stuff is made on what is called "the basic case", a 30-06 before sizeing and necking down. So you don't have to ream the case mouth. I have all the loading data or I think it was still listed in Cartridges of the world #8. Maybe some older reloading manuels will have it also.
It was a REAL hand full in the Combatmaster. Sid Woodcock told me that it was never intended for the small guns but the customer knows best so they made them. He also said that when he shot it after about 30 rnds it would start jaming and then he let his hand take a break and would function fine again! Speaking of Mr Woodcock I have his email and will send it to you.
Hope this helps.
L8r
Conley