I am still using 10w40 in my 88 4g13 basically the same engine.
It is not about how old the engine is it is about how it was overhauled. I overhauled my 88s engine at about 220000 kms and she is now over 330000 and I have done a major restoration. But j tried to use the max OEM specs parts and with the repair manual in hand..
Get it checked from someone who knows these cars.. and get it compression tested..