I currently have 4 machines covering a Six foot buy 12 foot space 72 sq ft on average they weigh less than 250lbs 1000 lbs total.
so 1,000 lbs divided by 72sq ft is a live load of 13.8 lbs per sq ft normal construction should have no problem supporting as many pinball machines as you can put in the room. All that being said looking at those structural pictures have an engineer look at it.