Gentlemen
all good information and thank you all very much for all the support and feedback. However Ive come across my first snag. The gunsmith I was going to use in Sth Aus does not have a set of 358 reamers, does anyone know of any gunsmiths in Australia that might have the skills (and reamers)to do the job?
Im going to re-barrel but obviously Ive got to get the barrel chambered correctly and as said, the gunsmith I was going to use does not have the reamers.

Also does anyone have any thoughts about twist. I like a heavy projectile so Im going to go 250 grains and was thinking 1:12 but would I have to go that tight?
Cheers and thanks in anticipation