Are you sure the deck doesn't drain into the splashwell ?
I wouldn't want the deck to drain into the bilge but some boats might be designed like that.
Mine self bails into the splashwell then drains out the back.
Enough water finds its way to the bilge as it is.
I would consider adding a second bilge pump with an auto float switch wired direct to the battery,
500GPM isn't much, they don't really LIFT 500gpm, thats just advertisement.
You're way under capacity as things stand now.
I installed my auto switched pump 6 inches higher than the other pump so its not constantly flicking on and off from water in the bilge and stays out of the flotsam junk that inevitebly accumulates there.
Heres a good bilge pump primer.
http://www.yachtsurvey.com/bilge_pumps.htm
Great looking classic anyway.