I understand your motivation to do a shoe lump construction but I am afraid you will run out of room between the barrels and the shoe lump, plus, unless you have made one before it would be quite an undertaking to get into without previous experience. I have a friend who is doing one right now from scratch and he encountered all kinds of problems. He is an experienced double gun man, but it was a chore for him, even with all his experience. I'm not telling you it can't be done, but I do think it would be very difficult, especially if you are building a .577 or bigger rifle. If you decide to go ahead with your plan, contact me and I will put you in touch with him. I'm sure he would be interested in talking it over with you. Bob