Gazz.
It sounds like you're well versed in the use of tools. If the forend fit it too tight, take the metal off the forend lump on the barrels. A singlecut mill file is perfect for the job. Look at the contact marks and take a few thousandths off. Try the forend fit, remove a few more thousandths as needed. Contrary to what others have asserted, it's easy to tighten up a forend if too loose as well. Many a Perazzi and Krieghoff has had the forend lump on the barrels tightened up with a small centerpunch mark on each side of the lump, near the rear surface. If you go slow, tightening will not be needed. It's not a super critical fit and can be done by anyone comfortable with a mill file.
