Upgrading PIX 515 from 5.1 to 7.x

Hi

I have the opportunity to pick up a PIX 515 (non-E) with IOS version
5.1 on it. I already have a PIX 520 running 6.3 but want access to the
7.x environment which my 520 will not do. I know there are activation
keys that enable certain functions on the PIX etc but wanted to know if
these were required to upgrade the IOS on the 515 from 5.1 to 7.x. I do
have access to PIX 515e's running 7.1 and need to know if this image
can be easily taken from the 515e and placed on the 515 without need
for additional licence keys etc like can be done with Cisco routers.

Thanks