My slabs were 116x75 and they were huge and pretty standard size. My island is 48x96 and of course, I have no seam. I don't think you can get a piece at 140, sorry. According to my slab size (and I bought two whole pieces), you could get probably 110x70 out of one piece with no seam, maybe a titch less than that based on jagged corners, etc? Also, your sketch didn't load....

Like you, I have a very long island. I chose to make it 3 sections, with the middle section dropped a few inches, because I didn’t want my kitchen to look like it has an airport runway in the middle of it! Plus, it gave me the opportunity to turn the middle section into a baking area, very useful for kneading, stirring thick batters, etc. If you decide on multi level, it gives you the opportunity to consider different counter materials on the different heights, e.g. wood or butcher block.