Today, feeling a little concerned about the actual mileage, I rang the original bus operator - Calcasieu Parish Public Schools in Lake Charles, Louisiana. A very pleasant lady put me through to somebody's voicemail. With luck, they should ring back in the next couple of days. Meanwhile I emailed their director with information and questions.
I don't really care to go after the individual that altered the odometer suffice to say that if it was done illegally with intent to defraud me or the previous owner then I'll be happy to let the state take care of it all. All I want is to know approximately how many miles are on the bus so that I can compare that with the expected life expectancy of the components in order to budget for repairs and to estimate how much likely use I'll get from the bus before repairs are uneconomical.
In theory this information should all be held by the schools for at least 7 years and should be available under the Freedom of Information Act. Having said that, a cordial approach usually gets all the information very easily.