John,
There were three specifications of springs for the front and two types for the rear. (this is using a 1929 - 50 Chevrolet Parts Book)
The fronts:
1939-41 (except JB & KB) 1310 lb. tension had sire diameter of .576-.580 with white paint down the length at the same arc of the spring) Part # 3653059
1940-48 (/exc. KB) 1600 lb. tension and had a wire diameter of .608 - 612. Paint was blue. Part # 5246233 (I have seen that these were for heavy duty.
1940 - 48 (exc. KB) 1375 lb. tension and wire diameter of .585 - .589) Paint was green. Part # 3664086 (I don't have a clue as to why they had this size)
The Rears:
1940 - 50 (1941 16 inch wheels, heavy duty, covered) Part # 605383
1940 - 50 All with covers Part # 605374
Over time the springs both front and rear will loose tension. Two remedies come to mine for the front. A spacer that can be inserted in the wire coiled space or a washer in the bottom of the A-frame or replacing the spring. The stronger tension and wire diameter will tend to keep the height higher then a lesser tension ones with smaller wire ones will. That is obvious.
The rears ones may see some longer use by using longer reach shackles. The heavy duty 8 leaf springs will tend to take longer to sag below a suitable level. But, as in the front they may initially seem raise the car a bit too high.
The basic Chevrolet parts places have replacements. You may also look up the wire companies and have them cut you a set at a lower price. You'll be able to specify the diameter wire you want.I'm getting a little out of my area here.
A 1941 or other year parts book may list different information but basically I doubt the part numbers will change.
Covered rear springs are getting hard to get.
Good luck,
Charlie
BTW: There is one other thing in the 1941 that has a heavy duty application and that is the clutch assembly from and including the fly-wheel, disc, pressure plate to the cover with spring. All heavy duty.
