Hi Peter,
I suggest you also join the VCCA forums.
https://vccachat.org/There is a LOT of information on the 1912-1928 forum on the 4 cylinder Chevs. You don't have to be a member of the VCCA Club to be a forum member, but Club members have access to sections with detailed accounts on how to overhaul various parts which non members cannot access. I have not joined the Club: there is enough expert advice available on the above forum for most requirements.
I have owned several twenties Chev cars, and still own a 27. None of them had the chassis number stamped on the chassis: it was always on a plate nailed onto the passenger's side seat frame, which is usually missing on unrestored vehicles now.
There were several truck models in 1927 having different load capacities. The smallest (1/2 ton?) used the car chassis, and the heavier duty models used a more robust chassis. The LM was a one ton truck.
There are at least three suppliers of reproduction parts in the USA: who get favourable mention in the forum. One is:
https://www.fillingstation.com/Among other things they have workshop manuals for the various twenties car models - not sure whether these cover the trucks too. In any case the truck engines are virtually the same as the car engines, and blank chassis number plates are available to carry a new VIN number allotted by the DMR before registration. If it is an original truck engine the engine number will have a T prefix. If it has been replaced by a car engine, from memory the car engine number will have an R prefix.
Midway through 1927 two alterations were made to the car engines. I don't know if this applied to the truck engines too. The diameter of the valves was increased to the same as the 28s though the 27 and 28 valves are not interchangeable, and the distributor was changed to the type fitted to the 28s. this had a semi-automatic advance/retard instead of the wholly manual advance/retard on the earlier engines.
Check your cylinder head for cracks: the early Chevs were notorious for this, so much so that the factory made another batch for spares for 1926/27 cars in 1934. I know because one of my cars had one fitted. It was identical to the original heads except that it took 14 mm spark plugs.
Frank