The model 20 factory slide spring weight is 17 pounds. On the Lone wolf site they list the weight as being "stock" under the heading "slide parts"
Now obviously you would have to measure your spring in relation to the slide length to be correct. Mine, stock length, at 17 pounds is 3 1/4" long.
Yours will be much longer I'd imagine. I would give Lone Wolf a call and see what the numbers on yours (stamped in the guide rod) will work out to in weight, overall, they can get you fixed up pretty cheap.
I have invested in a heavy tungsten guide rod and factory weight spring for the time being, but will be absolutely upping the spring weight when reloading for the higher velocity ammo.

Here's Lone Wolf's Page...  http://www.lonewolfdist.com/Default.aspx

And their Number...  Telephone/Fax:
Phone:  208-448-0600
Fax:  208-448-0601

Hope that helped a little...

Hey Al..! good to see ya here, I just got signed on tonight... You have got to see some of the revolvers over here, I'm speechless. Looks like a good forum..! I forgot to add that it was Osageid from G. Pro that directed me here Al, Thanks for the reminder..!     

This is FREAKIN' NUTS..! 
We just passed concealed carry here and now there already gonna start this kinda thing..!
AARRUUGGHHhhh..! I'll be on the phone Monday to find out more on this one..!

Quote from: MCQUADE on September 07 2013 06:57:20 PM MDT
Welcome JeepinDave!!! Thank you for your service too!! I'm 44, former military also, many, many years ago. You will find a lot of great and useful info here.

Thanks McQuade... still goin through the stuff in here, I am quickly becoming a fan of the little AR type/Glock hybrids, and about to check out some revolvers, there's some really cool stuff in here, I kinda though I was going to be out on my own when I picked up my 10 mm. but I am pretty happy now..!

Hey all, I'm new here, but I've been around on another forum building a G20, Which I have come to love more than my previous .45 autos, Which
had served my purposes just fine in the past. I had to sell them to finance a custody battle and upon winning went shooting with some old friends, needless to say toys I had never seen started to pop out of the woodwork and I started to buy a collection again, I started with the Glock model 20... I'll post pics soon, Just kinda ill at the moment.
I haven't really had a chance to go through the forum and meander yet, but I'll get to that this week.
I'm Retired Military, 43, and gettin' younger everyday.
Great to be here