No.
20W50 will be slightly thinner at low temperature than SAE 30 - which is a good thing, as all oils are way too thick when cold, which is where most of the wear and damage occurs.
It may be slightly thicker at running temperature than SAE 30, which is arguably not a bad thing on an 'old' engine, especially if it is driven hard.
The major advantage of multigrades is better flow under cold starting conditions than straight oils. That's what they were developed for.
20W50 will be slightly thinner at low temperature than SAE 30 - which is a good thing, as all oils are way too thick when cold, which is where most of the wear and damage occurs.
It may be slightly thicker at running temperature than SAE 30, which is arguably not a bad thing on an 'old' engine, especially if it is driven hard.
The major advantage of multigrades is better flow under cold starting conditions than straight oils. That's what they were developed for.