There are ways to quilt your tops in sections, using a DSM, even if the tops are already finished. You can divide the batting in sections. This is one of the methods described in Machine Quilting in Sections by Marti Michell. Many people also manage to quilt large quilts (without dividing up the batting) in their DSMs, but it does take some practice. You can also put most DSMs on a frame, which makes the task somewhat easier, but again you will want one with a larger throat space.
This lady claims to have a vintage longarm, and it does indeed look like her machine's throat may be longer than the standard vintage machine, though it's hard to say for sure.
http://busyhandsquilts.blogspot.com/...g-machine.html