According to the shop manual, the aluminum piece that used to stick out there is the "timing chain protector". As far as the timing chain tensioner guide and tensioner itself goes there is absolutely no problem with slack, when the tensioner is in place and fully ratcheted out. That piece probably would've prevented my timing mishap as there would've been less slack in chain with tensioner out (I think the chain hangs over that piece with tensioner out to prevent what happened to me), but after I fix the problem I'm not going to let any slack in chain, and replace the cover ASAP.
BTW, I cold welded (JB Weld) that hole up. I'm crossing my fingers it holds when put back in action.
'91 300E, 208k miles