If you want to go for a cafe racer tail then probably it wud be better if you go for a smaller and taller fuel tank.
Low Rider Cafe Racer Inspiration:
In the image you shared above if you notice the frame is lower where the seat is, therefore bike has a low seating position giving the bike its distinctive low rider shape. It also makes the bike lengthier.
Low Rider Cafe Racer Implementation:
Your Frame is straight and does not dip at the seating area. So you cant make the seat lower.....so to compensate you need to mount the tank higher and then match the height of the tail to the tank. This will give you a dip to make a seat. But I see a little problem in that......you have a 13 inch rim at the back and if you match the height of the tank and tail it will increase the gap between tyre and tail even further. In its current state its looking good and if you make the tail even higher.....Im not sure how will it look. You can make a better decision as you see it in metal.
Why Not THIS?
Its just a suggestion but I think it would be easier to achieve the shape in the picture below. In this case the tank is the highest point and as you get to the rear the height of the bike decreases, the seat is lower than the tank and the tail is lower than the seat. You already have a bada$$ long front end......it will look cool. Just a suggestion!