I would also tie it using pearle cotton, since it is more accurate of the times and would use an old wool blanket if you have it - that would be historically accurate as well.

I agree with dunster, I think the quilt look fabulous as it it and giving my opinion for what it is worth, tie it! Would seem more authentic!

I fully agree that to tie it would be the best and most period correct, I would back it with muslin, which would also be
the most period correct. Have fun and watch your father-in-law enjoy his new quilt.

I love it, as is. It adds to the authenticity of being a scrap quilt. Please don't rearrange it! Definitely tied with perle cotton. Your FIL will love the fact that you took so much time to make something this beautiful for him! Please post finished pics!

Do not use pearl cotton to tie a quilt. We used that as per the instruction of our 4-H leader, and within a few months all the ties were coming loose. I pulled each tie tight again and used Fray-check to keep them tight. I had made a second quilt at the same time and sent it to Kentucky with a group that were going to work at the missions. I can't get it out of my mind that I sent something that was going to fall apart in a short time. These people have so few nice items, I had hoped I was sending something that would be useful and would last.
I usually tie with yarn. If you use wool yarn, the more the quilt is washed, the tighter the tie gets.

Nice quilt,a meander quilting would look good on your quilt.I personally don't like tied ones.Tacking also is an idea.

I agree. It's great the way it is now. Love the choice of fabrics.

Your quilt is gorgeous!!! Thanks for sharing

Beautiful quilt. I agree with the tying. Have a camera ready to capture the look on your FIL's face when he receives his gift.