SPF is not the same as a PTR, and how would that solve your problem when you just stated that gmail doesn't accept email from servers that don't have PTR.
"FYI - google won't accept email via smtp over IPv6 if you don't have a reverse DNS v6 record for your mailserver's v6 address."
You stated that spf is not sufficient - now your saying it is?
"Having a valid SPF record with IPv6 included isn't sufficient."
"I managed to work around it by updating my SPF record to specifically include a v6 address."
If your isp supplies you with a /64 then they should provide the the ability to update your own ptr. Hurricane electric allows for this with the /48 or /64s they give you for free.
Who is your isp?