Is your red block insertion point position important to you, or it can be changed (now it's placed at ridiculous place that has no meaning IMHO)?
By changing position of blocks insertion point to for ex. lower left vertex of your rectangular shaped reference block, you'll be able to determine X coefficient and Y coefficient for matching destination rectangular shape you desire... Use command DISTANCE - pick lower left point of red block - pick lower right of red block (remember value); then use DISTANCE command and pick lower left of destination rectange - lower right and also (remember value)... Finally divide lastly remembered value with first one and that's X coefficient... Then just multiple X coefficient with X scale factor of red block and change that X scale factor to multiplied value... If red block had base point changed to lower left point and if that red block was placed so that lower left point (base point) matched lower left point of destination rectangle, after redefining X scale factor with calculated value (* X-coefficient X-old-scale-factor), red block width should be matched with destination rectangle width... The same can be apllied and for Y axis calculation... So finally you'll get red block matching white rectangle like you asked...
For changing block insertion base point, look at
www.lee-mac.com and search Change blocks insertion point routine...
