Ok, I have returned to working on it... I got a full node of another chain running and set this node as sole peer of the altered prototype. Now it reports bad header formats and PoW, as it should since the coin I am altering the client to work with has two - and an extra byte in the block header to signify which PoW is used on a block.
I have to do some forensics on the blocks of the foreign chain, split the logic so there is two PoW difficulty consensus values and the recognition of valid PoWs, but I am making significant progress. I most likely will, at the end of this process, be able to precisely point at which parts have to be changed to cope with a different network, and which for different chains, I have the idea of shifting all those functions and settings into a separate library so it becomes possible to quickly target a new PoW coin using the Gocoin codebase.
https://github.com/ParallelCoinTeam/duodThere is a working docker version of the circa 2014 parallelcoin in there, likely you could easily substitute any other for this purpose. I set the configuration from the gocoin side to connect only to this docker instance. After it grabs 20 incorrectly formatted blocks it complains and stops syncing for a bit, tries again, complains again... If you changed which coin was built in this you could make it work, change genesis block info, PoW verification, difficulty adjustment policies, etc.
