@camen though the members here are very helpful and generous with their knowledge - no-one is going to say 'yes that's all fine, go buy it!' If you're not sure and buying online without any direct contact with the dealer then wait and be sure. At that price you will find other late 1970s Speedmasters without too much trouble. Don't feel under pressure.
if it helps, here's a pic of my 145.002-76 Speedmaster which you can use as a reference. Your 78 example would be the same as this - tritium hour markers, T next to Swiss Made (at the bottom of the dial), long 'S' in the Speedmaster font, no step dial.
As previously commented - the tension ring looks quite dirty, whereas the dial itself seems very clean. The tritium in the hands also look less aged than the hour markers. None of the things are necessarily deal breakers and only based on the photos supplied - but something to be aware of.
There are various sites online where you can check if the serial number on the movement is correct for that reference (145.002-78 as it says on the inside of the case back) A quick check shows yours is from 1980. This would seem about right as this reference was manufactured for a couple of years I believe - but do check several sources.
The case on the left hand side does look over polished, some of the crispness to the edges seem to have gone.
Sppedmaster 101.com is the place to do your research
