How to adjust timing if you can't see the timing marks?

As above..........Find an area of the balancer you CAN see, even if underneath. Fabricate a new pointer and mount it with whatever bolts/ hardware are acessible, pan, timing cover, etc. You want the pointer somewhere that you can see it and the balancer.

Now use a piston stop to confirm TDC is accurate on the original setup.

Last, just rotate the engine to accurately align with whatever mark or two that you want for timing, and scribe/ paint a new mark opposite your new pointer.

OR if you can set timing fairly quickly, run engine BRIEFLY and set timing with the belt off.