Step 1

Found a disk version of Manic Miner for MSX on some emulator site. The game is divided in three files, miner1, miner2 and a simple loader in basic.

The loader loads miner1 to $8c8c and executes it. Then miner2 is loaded to $891c and executed. I tried loading miner2 directly and the game ran just fine so im gonna ignore miner1 for now.