Re: Remington 550-1 scope mounts
Phil, I think I have never seen a 'factory' drilled 550.
But, if there is one hole forward, and one aft, of the ejection port (per your 'two hole' remark, this was for a one piece base; if two holes, each side, a two piece base setup seems reasonable, but the spacing, c-c, is the clue; the receiver is cylindrical, without taper, so either a one piece, or two piece, base setup would be easy to do, but a two piece approach normally involves four holes, not two.
Could this rifle, assuming the two holes at the backside (Behind the ejection port), have worn a receiver mounted Micrometer sight, at some time, and used the original front, for aiming?
Don't start no s**t and there won't be none, Terry