Try contacting the people that make MAB barrels. I have used a MAB barrel to convert my 550 Safari Magnum to 404 Jeffery, and they did a great job.

http://www.tsengineering.com.au/

Give them a call, they may be able to put you on the right track. Otherwise I can recommend Pine Rivers Lock and Gun for you to discuss your requirements. They doa good job and could let you know what are the best options.

www.prlag.com

Good luck!