Upgrading DD-WRT on 3500NLv1

So I recently took the opportunity to upgrade my Netgear 3500NL v1 to the latest DD-WRT firmware out there:

DD-WRT v24-sp2 (03/16/12) vpnkong
I had been running an older version, I believe it was a MEGA build (DD-WRT "Mega" BETA svn 14826 (2010-07-18) for WNR3500L), but decided based on other changes in my network - why not go the whole hog.

Unfortunately there were a couple of issues:

1. I couldn't use my previous settings, since the port forwarding rules were not impoted correctly.
2. Filter WAN NAT Redirection seems to be broken and required a workaround

The following firewall script was required, under Administrations | Commands:

iptables -t nat -A POSTROUTING -j MASQUERADE

This worked around the Filter WAN NAT Redirection problem (it doesn't appear that I can disable it)
Point 2 specifically prevented me reaching internal services that had port forwarding associated with them.