For anyone still following the trail, a few small items:
1. There is a Nov 1805 London Gazette bankruptcy entry for a Moses Marcus Levin (names in that order), Leadenhall Street, London, merchant.
A follow up entry Jan 1806 describes him as 'merchant, dealer and chapman'
Then in Jul 1811: 'Moses Marcus Levin (committed by the name of Moses Levin) formerly of Leadenhall Street London and lately of Norfolk Street in the Strand, in the County of Middlesex, Merchant, a person against whom a commission of bankrupt has issued, and is still in force ...'
2. An 1809 list of voting members of the East India Company lists Mr Moss Levin, Paradise Row, Chelsea.