I picked up an early war Irvin a few years ago that had literally come apart at the seams. Every piece of thread had rotted away and I had a pile of pieces - a complete Irvin, but in pieces. A good friend of mine, who is also a skilled tailor, re-assembled the jacket using appropriate thread and re-using the original needle piercings with fantastic results. It has some wear marks, and a bit of light soiling, but it was worth the effort.
It is certainly possible, with considerable care and effort, to bring this Irvin back to life. If it is going to be an important addition to your collection, it will be worth the work.