Hi guys I just need some guidance on the following?

I know the question has been asked before, however I couldn't get the right answer to feel at ease. I do not have the money to buy the coilovers as yet, so I am also intending to use just a piece of sqr tubing for now in order to finish the project. I have done some searching and came up with the following and please tell me if it will be fine this way.

Coilovers Brad sells are the following: 13inch open and 9inch closed with a diameter of 1.9inch.

If I want to get the disctance that the brackets should be from each other I did the following calculation:

13 - 9 = 4

4 * 2 = 8

8 / 3 = 2.67

13 - 2.67 = 10.33

Therefore the disctance that the brackets would be from each other would be 10.33inch. Does this make sense?

Now I would obviously have to make sure that the coilovers will not foul against the top wishbone which hopefully I get right. However the most important question from me is the following: If I set the chassis at ride height (125mm front, 150mm back), do I then make sure that the bottom wishbone is parralel to the ground and then weld in the brackets that will be 10.33inch from each other? My concern is that if I do this and I eventually fit the engine that with the weight the bottom wishbone will not be parralel to the ground anymore.

(I must be honest that when I take a ruler and measure 125mm from the ground it looks really low.)

Maybe this is a stupid question, however I am trying a build like this for the 1st time.

Thanks guys