At second glance I'm impressed with how clean the outside of the lower intake manifold is, and a lil shocked how bad the valve train and valve cover insides are. Is this really just neglect/cheap oil?, I know it seems to pop up on the 5vz-Fe here from time to time, I must have got lucky all the old 5vz-fe's I opened looked like new inside with a slight stain, I don't consider what I'm seeing above good and a compression test would be my next thought, the hard part is cleaning it out, most say just run Syn oil and hope it cleans out, as that's where the flush can become risky ironically. I hope you get it sorted out, sometimes the less you do the better after 20years.