With the LPG, it's easy to get a second LPG filler nozzle fitted in parallel with the Marine one, just contact a local LPG installer, then you have best of both worlds.
Alistair there is alot of rubbish spoken about OMC,mostly by people who have never owned one.
The engine in the boat you are looking at is made by GM and will be the same engine as used by Merc and VP.
The Cobra drive was a very good drive once it was sorted, but suffered from early problems that gave it a bad rep. It is also very sensitive to having the gear shift cable set up correctly. Volvo took over the drive, still calling it the Cobra for a while and I beleive that in some senses it still exists,although by now heavily modernised, in the Volvo line up.
I owned one for a number of years that outlasted the GM based engine and I would definatley have another one. Easy to work on, clever positioning of Impellor for easy changing and in my opinion, very reliable.
Don't be put off a boat cos it has OMC, lots of others will so it may make it a bargain. Parts are easy to get from the states and cheap as chips compared to buying UK sourced spares for other makes.
For the work that he says has been done on the engine, drive oil looks just about empty which would be a worry, and the belt looks like its not been changed for a long time.
Since engine is most costly and based on the feedback would say walk quietly, but thats just my view.