Looking at the framework and plans for a Timberwolf. What problems can anyone see in making the rear end a " hardtail ". Up here parts are hard to come by. And what's the pitfalls of fabricating the parts from raw stock ?
The main rail is a long beam. I suspect the rear suspension takes a lot of force out of that beam. All the force that goes into moving the suspension will go into bending that beam. Having said that other deltas in the range use a solid rear. It's hard to see how a std mountain bike pivot and suspension unit would be too hard to find in most places but could fairly easily be made from other parts such as a pair of rod ends for the pivot. If you go hardtail I suggest triangulating the rear from the seat post to the axle area then a bit of reinforcement such as gussetts at the base of the seat post where all the loads will gather.
I have the plans for both the Timberwolf and the DeltaRunner. The frames are similar in that they have the same back end (Drawing 1 in the TW plans) and are made of 16g 1-1/2" square tubing but the DR has a solid 60" main beam and the TW is two piece to incorporate suspension. Both the TW and DR have 26" rear wheels on 5/8" axles but the DR also has a 26" front wheel compared to the TW's 20" front wheel. So this kind of makes the DR a hardtail version of the TW with over seat steering and a 26" front wheel. Given the similarity of the frames, I would expect you could start with a solid main boom on the TW and cut it later to incorporate a pivot.
Here a couple of pictures of the DR from the AZ plan page showing the solid main boom and a closeup of the rear frame.
If you still have concerns about flex/support with the 60" span on the DR, I would point out that each of the main beams on the Kyoto cruiser is 68" long so there is precedent in the AZ plans for going even longer.