I don't think there is a recommended replacement schedule for the timing chain. My haynes manual just says if there is more than 1/2 inch of chain deflection (measured by pushing the chain all the way to the left then all the way to the right) then replace the chain and sprockets.
I'm not sure what you mean by tighten the valves. Do you mean lapping the valves, or are you talking about doing something to the push rods or rockers?
2000 Jeep Grand Cherokee V8 Stock
93 YJ I6 hard top (really belongs to SPEED)
RE 4.5" Extreme Duty Lift, Advanced Adapters SYE, Tom Woods CV Drive Shaft, EA589 10" rims with 33" x 12.5" MT/Rs
Bullet Proof Front and Rear Bumpers and Tow bar