I cross referenced the two models and heads and cylinders have same part number . Mine are silver but found a MS 620 head on ebay that appears to be silver but most a dull blackbare head is same part number across all years m620 and mts620.
if you go here - Ducati Spare Parts - and put in your year and model, you can bring up the parts listing. then, if you scroll down to the part number list and click on your part number, it will bring up a listing of everything that part fits. if it's an old model you also get superceded models listed, so a part i know had a different # on say a 1991 900ss will show up on a 1198 list with the 1198 part # if you like.
clicking on the part number in the picture will get you the price and their stock, but the number in the diagram listing below gives you the applications.
sometimes if you see variations in the end letter it's a colour thing, and if for instance you knew monster heads were silver and mts heads were black, that'd be it if all the numbers are the same. frames are also like that, wheels, etc.
anything mts 620 will be cheap i expect. they're about as desirable as the plague. pity, was a pretty fun little bike.