There are two 90-T updates. The first involves the angle (8 degrees vs. 10 degrees) of the locking lug. A 90-T owner doesn't need to concern himself with this item unless or until his 90-T starts popping open when fired.
The second update involves the forearm. There's probably a better description for this issue but suffice to say that the forearm latching mechanism is one of the very few flaws in the 90-T design. It will sometimes break. If it does, its a b!tch to deal with.
You can see a photo of the completed forearm update on Doug Braker's website. Doug posts on here as GunDr.
The link posted above should take you to the page titled 'shotgun action work'. Check out the photo at the bottom.
PS: Mr. Braker has forgotten more about 90-T's than most good 'smiths will ever know. I'm one of many satisfied customers that recommend him without hesitation.
I agree with recoil sissy, Doug Braker is the Man For ALL types of Gunsmithing but, is an artist with the 90T. SMOKE, i have a couple of 90T's but, they are low rib guns and expensive. Bev Davis has first choice on one but,i have not sent her pic's yet. Doug advises no need to worry about the forearm update, just shoot the gun and IF the latch breaks he can fix it. joe90t