Downloads for R75.47 are under this sk and details of the last developed HFA are here. But it looks like TAC needs to supply this HFA.
If you are going to use the same physical / logical interface layout, you can probably do a save configuration on the old GW and do a load configuration on the new one. If the Interfaces won't map out the same way, you'll have to recreate your network topology via WebUI on the 4800. I'd do all this just connected locally to the 4800 via a laptop or console and not on the network so you can assign the same IPs.
Once the GAIA config is set, edit the GW properties in SmartDashboard and reset SIC on the existing Gateway object.
Disconnect the old appliance from the network and connect the new one in its place. Re-establish SIC with the new Gateway. Perform a "Get Interfaces" to pull in the correct network topology. Push policy to the Gateway.
You should be back up at this point on the new GW.
It is probably worth throwing out the usual disclaimer that this CP version is unsupported and the 4000's are end of support on 6/2022. Support Life Cycle Policy
R80 CCSA / CCSE