Genealogy / Family research Plock - Marks (Markowitz etc) Family [7]

My grandparents came from Plock (Plotzk) in Poland. I'm looking particularly for their marriage which would have been 1898 - 1900 and would I believe have been in Poland.

They left Poland for the UK sometime just around the turn of the 20th century but I don't know exactly when. They adopted the anglicised name of Marks. My grandfather was Eli Marks and grandmother Dora Marks.

My grandmother gave her former name (meant to be her unmarried surname) variously as Marcowitz, Markowitz, Markovitch, Marcovitch and Markowicz. However, I wonder if she misunderstood and gave her Polish married surname instead.

Would her unmarried surname have been Marcova or something similar I wonder?

Is there any online source where I can look up marriages in Plock for the period say 1898 - 1900?

I'm also looking for my uncle Maurice Marks (their son) who was born in 1900 or 1901. According to my grandmother he was born in Manchester but he doesn't appear in the UK General Records Office index. I therefore think that he was born outside the UK and probably in Poland.

If anyone can help by indicating where I might get further information I would be most grateful.

Steve