Cliff, they are longer, but alot thinner. Old spring is 0.09, new spring is 0.06 on my calipers. I got some shim stock from work, going to fiddle with that before I try Hawk's way. New springs have near zero tension on them.
That may not be a bad thing the old ones were pretty stiff anyway, I thinned and narrowed my Uberti 76 mainspring slightly for smoother action. I know these are not like main match guns and you want a good fast snap to the hammer for accuracy but I still don't like an action that gives a workout.
There may be some that cringe and have a fit when I tell you this but if it was mine I wouldn't hesitate to bend the spring right near tension screw. I trust that more than having shim in there that could pop out.
Look at Greyhawks pictures above, you can see the bend in the spring on his. Some are like this and some are not and I'm almost willing to bet those bends are added when necessary upon factory assembly.
I added a bend like that to the mainspring on a rifle of mine years ago and it's seen well over a thousand rounds since then with no issues. Others mileage may vary but never has given me any issues.
Edit, if you attempt to do that I wouldnt put it in a vice and bend it because you can put a sharp stress area in it. I did it by putting the spring on a piece of pine and using a round brass punch where I wanted the bend and hit the punch with a hammer. You don't want to put any kind of sharp pinpoint stress area and this creates a radius to the bend.