It is rather easy to tell if the t-chain is loose, pull the valve cover and grab the chain, if there is any movement at all it needs to be replaced.

You don't haveto remove the head to get to the guides, though you will have remove the fan, t-chain cover, the front 2 bolts from the oil pan, the hidden bolt from the head to the t-chain cover, and I believe the crankshaft pulley as well. If the t-chain breaks and you are unlucky it will likely cost you more than a new t-chain and guides, i.e. broken/bent valves, punctured piston head, bend piston rod or crank shaft, etc.

The '93 FSM at the top of the forum will work for the '86 runner.

If it is the knocking type diesel sound the valves probably need to be adjusted. A rod knock on start up would be constant low knock-knock at idle, not the higher pich deisel knock. Picking up the stethescope from HF wouldn't be a bad idea, it is nice to have around from time to time.

With any used vehicle it is always wise to do a complete tune-up yourself before putting many miles on it.