Hi Julia,

At 802yds for four ounces the yarn is 3208yds per pound, which is similar to 16/2 cotton, so about half the weight / grist of 8/2 cotton. You could use it, but it will be thinner than the 8/2 warp and you'll have to be careful to not beat too hard as the linen weft could squash down easily.

The best thing to do is to weave a small sample, cut off, and wet finish it. Then you can see how it reacts in combination with the 8/2 cotton warp, and decide whether to continue or not.

Alternatively you could turn your outermost threads into floating selvedges and weave the linen in double picks in each shed, to make it closer in weight to the 8/2 cotton. I'd be tempted to try it first singly for a few inches, then doubled for a few inches, then cut off and wet finish to see which weft treatment you prefer.

Happy weaving, and let us know how it went!