Legacy blackfin and Blackfin+ are from different family. The software changes are as follows:
i). Interrupts - The 60x and BF70x has System Event Controller to control the interrupts, which is different than previous processors. so all interrupt assignment, enabling, and ISR code will have to be examined.
ii). DMA Channels - The DMA channel assignments are different in Blackfin+, so need to look at any code which refers to a specific DMA channel.
iii). Pin Multiplexing - The pin multiplexing is different, so any code that sets up or accesses pins may need to be changed.
iv). PLL & Regulator - The support CCLK and SCLK may be different, as well as the register bit positions. Make sure to look at PLL and regulator code carefully.
v). Boot modes - The boot stream headers have changed so make sure to get the correct settings in Project Options.
This isn't meant to be an exhaustive list, but should give you an idea of the major things to check.