How to rescale group based on a section

Wut,

I believe the simplest way is as follows:

1) Select the whole Group Blue Silo,

2) Object>Transform>Scale, then insert the following in the Uniform scale box: 600/5.9983% and press Enter,

3) Reposition the Group if needed.

This will increase everything by the quotient 6/5.9983 which will bring the with of L/U up to exactly 6px.

The use of 600, or 100 x 6, is because the scaling works in percent.

Illy (job description Adobe Illustrator) can make such calculations for you, fully/even more accurately than you can do it by inserting calculated values, and she is always eager to help.

Edit: I just posted after seeing the screenshot, then read the answers by Monika and Met.

And with this small number, (6px) no one will be able to detect a difference.