250 single racer

Hi All
Just taken delivery a 250 single racer and joined the forum straight away.
I was wondering what its based on as there is no frame number and I’m guessing the engine number may not be the actual engine it started with.
Is there anything frame wise that I could determine the source bike and then possibly the year.
Incidentally the frame is painted black, most racers I have seen are red, does this mean its a Monza?

Any help appreciated

Most racebikes seem to end up being a bit off a mix of parts. If the frame has no number stamped on it,it could come from America as they used a vinplate. The engine number should tell you what the crankcases originally came from.also the cases have a number stamped on the bottom of the cases both sides should be the same number if they originally came together.put a picture up,

Many thanks for your reply, further research and some chalk haas revealed the following frame number of DM250 81547 IGM 1985
Engine number is DM 98447