I think down to 120-130 mm it's quite easy to find a Headshok stem. Shorter than that, it takes time. The current looks like 150 mm?another thing, shorter stems for headshock/fatty with 1.56" diameter are also hard or at least expensive to get.
Obviously what we can see from the picture the frame was to large for the current owner and stem to long.
In all honesty the F2000 above is probably a better option for a project, the F500 you would probably sell or recycle most the parts anyway, depending on the your project needs and what you desire. I still think the F500 would be a great project to work on, I guess it all depends on how far and what you want to achieve. I hope you get a good deal on the F2000 if you decide to purchase it.After looking at the comments,i've decided to give this a miss.....however...i came across this f2000 frameset with fatty sl fork. Asked alot of questions and seems good to do a deal for £80...albeit waiting for more pics of under the boot to confirm its corrosion free. Not worried about paint cond too muchView attachment 802652