Some things are very obvious such as non-original or reconed speakers, non-original transformers, replaced pots, re-tweed, re-tolex, re-grill, etc.
and these changes are often disclosed and of a non-malicious nature.
On the heel of the neck should be a penciled or stamped date with a month and year that it was assembled in.
Other areas that contain Serial Numbers are on the top of the Neck Plate and the front or back of the Head Stock.
Leo soon realised that amplifiers needed to be sturdy to withstand the life on the road, and decided to build his own, to care for the needs of travelling musicians such as his customers.