Hi everybody, I was thinking about this in class today and felt you wonderful people would like to tear this idea to shreds. Mild disclaimer - I am 23, so any of my knowledge of Bird has come from hours of watching various youtube Celtics games and various highlight reels.
So here it goes. I believe the value Bird would provide offensively as a small ball 5 would outweigh the defensive lapses he would create by the nature of playing out of position. The offensive positives are too vast to delve into, so lets focus on defense. At 6'9" tall, he would actually have the height to not give up much size on that end of the floor. His playing weight of 220 (lets for a second assume he would play at this although with modern conditioning programs it wouldn't be a huge leap to assume he would be stronger and heavier) is low for typical small ball centers. He also lacks the leaping ability to make up for his lack of height in regards to rim protection.
But- Larry Legend was tough as nails. Everyone who has ever even discussed basketball knows that one fact about Bird. I think that he would at least be able to hold his own in one on one scenarios against most centers due to resilience alone. Larry would also be considerably quicker then most centers and could wreak havoc in the paint by stripping the ball and getting into passing lanes.
Also he could rebound like a center. Enough said.
Summary: While Bird would most likely be a small net negative at the 5 defensively, I think that would be overshadowed by his shooting/passing/driving ability at a position that isn't very skilled at the moment.
PS- This isn't to say that his best utilization wouldn't be a power forward (now) but I think Bird could hold his own at the 5 in super small ball lineups.