They're blades. They're practically the same whether they're from 1980 or 2024. The only thing they do is move the CG around but won't have any noticeable effect to you unless you strike it like Tiger Woods. They also have ground the soles so the turf interaction is different. Likely something the average golfer wouldn't be able to notice unless... they strike the ball as consistently as Tiger Woods.

The Pros will notice differences, but they are so consistent they can tell when the club interacts with the turf differently. There isn't ground breaking change in performance between a blade from 2024 and one from 1970.

You can only tell a significant difference in feel if its a different manufacturer that uses a different metal.

Yep - blades are blades.
Based on specs, 620s are 1* stronger lofted (not much overall) and maybe they've changed bounce, offset and CG slightly.
I would definitely have the lofts and lies checked on those 670s, so you can be confident they are as you would expect.
Nothing worse than struggling with them on the range, thinking "I can't hit blades", only to later find out specs are way off.

Good luck - enjoy the journey!