You Need To Take Some Measurements
Eghad, let me begin by saying that I cannot specifically tell you which size site to buy. Every rifle and front and rear sight combination often have critical measurements that may need to be taken in order to decide which size front sight is optimum for your needs.
For instance, how much higher is the mounting area of your rear sight from the plane of the top of your barrel, where your front sight will be located? Is your barrel tapered or not?
If you buy a sight that is a little too low, you are going to be shooting higher than you'd like and then you will need another sight or a ramp. So, you may be better off buying a sight that's too high rather than too low. If you buy a sight that's too high, your cheek might come up off the stock more or you may run out of height adjustment, (which I doubt in your case unless you are shooting really long range!).
But the point remains that you want to buy as close to the next highest size as absolutely necessary to keep you sights "inline" (on the same plane) for short range shooting before your bullet starts to rise very much. (So make it at least a little higher than necessary in front).
I don't know where you are mounting your rear sight. I can't take the measurement of how high it (receiver?) will be from the top of the muzzle end of your barrel.
When I visited the Brownell's website to look at your rear sight, there was a box at the top of the page labeled "tech talk". When I clicked on it, I noticed another box labeled "sight height calculator".
Here it is:
http://www.brownells.com/aspx/NS/GunTech/sight.aspx
The problem is, it doesn't take into account the receiver height if that's where you rear site is going to be located. You have to try to figure that out, and add it into the calculation.
If you can't, they do have a way to email questions through Tech Talk.
Also, I checked out this gun sight company which installs sights as well as offers sighting in services (relatively inexpensively too). You can also ask them for advice on which size sight to buy. I personally think that you are going to need one of the highest ones, but you can always install a sight ramp if you select one that's too low. Or just send the gun out and let the sight experts do it all for you. (You may have to first install the rear sight yourself though, just ask them.)
http://www.williamsgunsight.com/gunsmith.htm
http://www.williamsgunsight.com/
"Williams hopes the gunsmithing services and products mentioned throughout our web site provide you with many years of fine shooting.
Should you have any questions call our gunsmiths directly at:
1-800-530-9028 between 9am and 6pm E.S.T. Monday thru Saturday"
Or else maybe you can find a local gunsmith who can help you to take all of the correct measurements, or locate a fellow SASS shooter who has installed similiar sights who can assist you.
Good luck and let us know how it works out.