I can see them using Spencer on the weakside. Will they? I'm not sure... but he certainly could play there.
At 6-3, 250 pounds Marinelli might see him as a weakside end. If so, that would put our current ends (and tackles) as most likely:
WDE - Spencer/Selvie/Mincey
DT - Melton/Kearse
DT - McClain/Hayden
SDE - Crawford/Bass/Mincey
Going into the draft, Dallas could literally use a high pick or two on either DE and either DT without blinking an eye. IMO, Tackle is the slightly bigger need.
If Dallas drafted (for instance):
Aaron Donald in round 1
and
Scott Crichton in round 2
then Crichton goes strongside to compete with Crawford/Mincey, and Bass goes inside to compete at DT.
The DT's would likely be Donald, Melton, McClain and Hayden/Bass or another draft pick like Caraun Reid.
Spencer/Selvie/Mincey would play on the weakside.
That would provide a lot of competition and versatility along the defensive line. If Spencer made it back ok from the injury, we would actually be pretty damn good at WDE. If he didn't, then Selvie/Mincey would likely provide, at worst, a solid rotation there.