1-5" seems like a very large range, any spacer will introduce a lot of extra flex and chatter into the column, the bigger the spacer the more flex you will introduce.
I'm curious as to what size table would need such a large spacer and what would be the point on such a low powered mill?
I see scope in the column mounting to gain an inch of clearance in that direction just through a redesign. An inch of clearance can give you two inches more travel while remaining centred.
There is a huge stiffness benefits if this works out, personally I think the resulting 6" of Y travel is plenty for a mill this size.
My X2 CNC Brain Build: http://www.cnczone.com/forums/showthread.php?t=61345
Gecko G250 wiring errors: http://www.cnczone.com/forums/showthread.php?t=68960