Rock,
I'll Jump in on this one. I do a lot of varmint shooting, and bench shooting with my XM.
First of all, stay with the Harris. Most of the others are pretty worthless, imho. If the Pod Lock is the same as the versa pod, it is junk. Anything with the compression type nuts are a waste of time and money.
Second, you might want to give consideration to the swiveling head type. I have owned both, and the swiveling is great, especially on the ground, where it is likely to be uneven.
As to the attachment, you did not mention what type of handguards that you are using, but you can get the adapter for the military handguards, or you can drill the hole for the sling swivel stud in other type handguards. I think that most Harris bipods work best with some type of sling swivel stud. You do not want this thing mounted on anything but your handguard (preferably free floated), if you are concerned with accuracy. Anything resting on the barrel will give you accuracy fits.
You will also find that with any bipod, with any type of attachment, your poi will change when going from a hard surface, to the grass. It may not be a lot, but it will be there. I generally work on the bench for load work, and some fun, but as I do not hunt or varmint shoot from a bench, I use the longer Harris, from a sitting position. It is not quite as steady as bench shooting, but it is better practice for me. I find that in the fully collapsed position, I can still use it for prone. My last Harris was just a little too short for sitting. The sitting style tends to be a bit too long for bench work. I am sorry that I do not have any model numbers or heights to give you, but I do not have my gun here.
What I would suggest that you do is set the gun up on the bench, with bags, get it into the position that you like, and then make a measurement. Then I would use some shooting sticks in the prone position, and get the gun set up for your height, and the type of grass that you will be shooting over. Make that measurement, and find the bipod that best fits. As you did not mention the type of grass that you have, or what you would be shooting at, it is hard to be more specific as to heights. Most of the lower BP's will work for prone and bench, but if you need to clear some tall grass, or cactus, or slope, you might want a little more flexibility in a longer one. The bench is fun, but not terribly great practice for the real world, especially while hunting or varminting. If your just paper punching, or can blasting, it all may not be to critical, as you will have time to adjust your leg screws, and get everything even. What I have decided is to stay with either the sitting or prone for all real practice, so that I do not have to worry about poi changes. My sitting bipod works well enough in prone. This saved my bacon a few weeks ago, while antelope hunting. I had a great prone setup, but when the antelope came into view, even the high prone was not enough to clear the grass and slope. So I just rolled over, extended my legs, and popped up sitting. One dead antelope.
The nice thing about the Harris' is that they attach via the sling swivel stud, and are quickly removed and changed. I have several, and that may be the best approach.
Craig