[Mike_The_Grad]

Maybe too little too late, but what the heck...
Yes, that is not the original timing chain. That is a "Roller" type timing chain.

Yes, that amount of slack is excessive. You should have no more than 1/4" of travel.
When I pulled the cover off my '72 SB 350, the chain moved almost an inch! But it started,idled perfectly,and smoked the you-know-what out of the tires...lol.

Also, yes it will affect vacuum and performance. I replaced my stock setup with a "True Double-Roller" Timing set at a tune of $35. The stock set was $17.
The toughest part of replacement is the crank sprocket,and only if you attempt it without the correct puller/installer like I did. Local parts store should be able to lend it out, other than that pretty straight forward, proper cam to crank alignment needs to be at #1 TDC. Also check crank sprocket for markings indicating "advance/retard/zero" installation timing. Anything driven on the street should be installed "zero" crank timing.
Just my 2¢.