Almost certainly a Flymo DM and, yes, that lever was the release for the tipping body attachment. Many of the Flymo cultivators were derived from the Norlett models but most (all?) of those had split chaincases . As has been said that welded chaincase is reminiscent of the Westwood Gemini.
Presume that the engine blower housing with the recoil is missing, but if it’s in a box of bits it should have the BS Model, Type and Code Numbers on it. The Code number will date the engine to the day of manufacture which will give an approximate build date for the chassis. If you have that, I have possibly got the appropriate DM illustrated Parts manual.