JEBar,
Clicking on your link, I got a "404" error and the page wasn't there. Might be something on my computer. Anyway, I just looked at the Henry page of the original bronze and CH H011 models. I'm not an expert for sure, but I don't think a wood forend grip would work on this rifle.
If you look at the picture of this rifle on the Henry site (that's where I think your link was sending us), the small "tab" that is right under the barrel just in front of the receiver is moved forward when you need to load ammo. You then "break open" the bottom half of the barrel assembly to load ammo. Once the ammo is in, you close the bottom half of the barrel assembly, and the spring inside will then move each bullet toward the receiver. Any wood forend grip would stop this tab and of course, stop ammo from chambering.
The only way I'd think a wood forend would work is if the Henry engineers could design a forend where that tab would "tunnel through" the forend and not be stopped. But I don't know if the true 1860 original was built that way...haven't look for those way-back-when pictures. Might be interesting to do.
Like I said, I'm not that knowledgeable about your question....above is only my "guess" from watching some Hickok45 videos on this rifle. The Hickok45 video on that rifle ---
http://www.bing.com/videos/search?q=hic ... &FORM=VIRE --- does show the tab moving as he fires rounds, and I think he even mentioned how he had to move his hand out of the way from holding the barrel.
Another good eval video on this rifle is on the Gunblast.com site:
http://www.gunblast.com/Henry.htm At about 3min 40secs, he shows how to load the rifle and you can see the spring and where the bullets ride under the barrel assembly. When he shoots it, the tab creeps toward his hand and actually wedges against it.
Anyway, that's my < 2-cents on your question.