It may be possible run the application on 10.10.3, but I don't think it will be the 'Safari 7.0.6' that jarooda needs because Safari is a wrapper, its guts are in the OS provided WebKit frameworks.
For compliance testing, which I am assuming is jarooda's motivation, it may be possible find an suitable version of the WebKit browser:
http://nightly.webkit.org/builds/trunk/mac/1
but if the specification says 'Safari 7.0.6' then I think that the only way to be sure is to be running OS X 10.9.4 (from memory) with Safari 7.0.6. Virtualisation is a very useful tool in such circumstances.
C.