I ran it on WinUAE no problem: Standard A1200 config with HD, unpack the game to RAM: then issue:
assign fonts: ram:diamondkingdoms/fonts add
Then run the program!
Another change I would consider - change the jump from a constantly moving up then constantly moving down into a sin wave so you jump upwards faster at the bottom. This might also make jumping easier as you tend to smack into platforms and fall down regularly - particularly on the first screen.