Bill,
If you want, I can maybe get you started off in the right direction. If you tell me what caliber and load you intend to use and the length of the barrels, I may be able to get you close on the regulating spread. For beginners I think it is best to use Ellis' method of making up temporary spacers out of aluminum and attach them with hose clamps to your barrels. The aluminum cuts much easier than steel so you can adjust the spreads easier. After you have it shooting to your satisfaction, then you can make steel spacers to replace the temporary ones.
It is perfectly safe to shoot the gun while it is hose clamped together, just as long as the breech end of the barrels are securely soldered into the monoblock and the forend hanger has been welded or soldered in. I shot one of my tightest groups with a 45-70 that was hose clamped together.
Two brothers were watching me as I took the gun out and got ready to shoot it, they laughed so hard I thought they might fall over, but they quit laughing when they saw the target. I was never quite able to duplicate that group when the steel spacers were soldered in. Bob