Re: Default Gateway not on the same subnet

Your public IP is 65.153.72.74, not 207.108.206.249.

interfaces {
    ge-0/0/0 {
        unit 0 {
            family inet {
                address 65.153.72.74/30;
            }
        }
    }
}
routing-options {
    static {
        route 0.0.0.0/0 {
            next-hop 65.153.72.73;
        }
    }
}

In order to NAT from the ip block they are routing to you you'll need to configure proxy-arp

security {
    nat {
        proxy-arp {
            interface ge-0/0/0.0 {
                address {
                    207.108.206.248/29;
                }
            }
        }
    }
}