Hi Phil,
You have a 1953 D-type. I'm not sure what the "H" means, it may indicate the fuel, or it may be a sub-breed of "D" type, I don't know. The lads over at stationary-engine.net might be able to help you there.
If you google "Lister Engine Dating", IIRC the first link is to the late Peter Forbes' page, which lists the pre-1951 serial number ranges for all Lister engines; there's a link on that page to the scheme they use from 1951-1975, and from there a further link to the post-1975 system. There's a direct link from one of the threads in this forum (the SR2 question I believe).