Wow. Really cool stuff. That poster from 1887 is priceless. I have subscription to the Free Press archives and here's a blurb from the July 4th, 1887 game. The photos don't show an overflow crowd in the outfield. No mention of an overflow crowd in the July 4th, 1886 story, however. Note the very odd rule of a ball hit into the crowd.
Detroit_Free_Press_Tue__Jul_5__1887_.jpg