It felt snug when standing, not uncomfortable. On the bike it felt more snug, almost supportive. Though i was only on the bike for about 3 min, I wonder if after an hour it would be different.
Is there an easy way to have some stretch panels sewn in?
Take a longer ride and see how it feels, you may be surprised.
With an older suit I doubt it would be cost effective to have stretch panels sewn in. If you took it to someone who specifically knows motorcycle leathers the cost would be high enough to deter the alteration.