Looking in Roy Bacon's book 'Villiers singles & twins' gives the following information.
For 1959 the 249cc Model 83 started at engine no.25/C - 16303 & the frame no. started with the letters ACT (you quoted AOT which is not listed as any frame no. prefix), could you have made a mistake - is the frame no. difficult to read?
The Francis - Barnett Model 83 is listed as a trials bike made from 1958 - 59, & was fitted with the AMC 250cc engine.