If I'm posting this in the wrong place, please point me in the right direction!

If you're reading this and you do consult for Mikrotik, I'm probably looking for you please PM me or reply.
Normally I deal with this stuff my self, but I've just simply wasted too much time on this already.

So here's the setup:

Satellite Multicast Source -> CCR1036 Mikrotik -> Huawei MA5683 OLT -> Huawei and Mikrotik Routers -> MAG255 STB

I have the Huawei Routers working fine by just bridging the multicast vlan through to a single port (port 4), but this has had a few issues and so we are working on switching out to a setup with a single port GPON ONU and an HAP AC2 router. My first thought was to use the IGMP Proxy which I got working, but came back the next day to discover that it wasn't working anymore. When I did a bit of wiresharking I discovered that the Mikrotik was converting IGMPv2 messages from the STB into IGMPv3 messages on the upstream. (no way of disabling this "feature") So I started looking into PIM, but frankly, at this point, I've wasted days on this and am just looking to pay someone to help sort this all out. So please shoot me a message if you think you might be able to help!
At this point we have about 50STB's actively using our TV Service.
Maybe it's just me but I feel like MK's implementation of multicast is a bit hit and miss.

Anyway thanks for any interest

Have you created a loopback bridge with a /32 IP address on it and add the IP address to the PIM RP
On the PIM interfaces you can change the interface IGMP version to the version you need.