I have a Brownell's curved 20 round body that I purchased a few years back.  I think Brownell's stopped making a curved 20 in favor of a straight 20.  Anyway, I'd like to put some guts in this curved 20.  I understand that a green USGI follower is what this mag was designed to use, and therefore imagine that a MagPul follower would work just as well.  What about springs?  Do straight and curved 20s take the same spring?  

Thanks

Those curved Brownell 20's were made for them IIRC. Predates them getting into the mag making business.

Anyway, attached is a pic showing a curved 20rd mag spring that is longer than a straight 20rd mag spring. The Magpul type followers work great in the curved mags but are a no-go in the straight mag bodies.

I'm counting 3 more coils in the curved spring.  It makes sense that more spring would fit in the curved body.  This all being the case, I guess I'll have to track down a spring specifically for a 20 rnd curved body mag.

44mag.com sells loads of curved twenties, bet they can get you springs.
Or cut a 30 to the right length as shown above.

My vote is cut a 30 round mag spring also as Uni-Vibe suggested.

Use the spring from that mag your are replacing with the 20 round "repair parts" Brownell's body.