Networks

I have been tasked with replacing our SonicWALL PRO 4060 running SonicOS Enhanced 4.2.1.0-20e with a different Firewall. The new firewall will use a SSL solution for VPN, but we need to roll out in stages. Is it possible to replace the SonicWALL with the new Gateway but placing it into the LAN, and then change the configuration of the SonicWALL to just accept the existing VPN policies? Basically I am wondering if I just forward IP Protocol IDs 50 and 51, and UDP Port 500 to the SonicWALL, will it function as expected? What else might I need to do or worry about?

Thank you in advance for your help.