Important to know if engine just seized sitting a long time. Or it seized while running.

Seized while running just put your other engine in. Simply put seized while running will usually mean really serious work. Now seized while sitting will not usually be too bad to get running again usually.

There are no absolute fixed rules in the above statements. Just in general that is the way it usually goes.

Your observed oil level means nothing as the first thing someone would do if the engine oil was observed low after an engine quit. Would be to add oil.

If you can talk to the last owner might help. They have nothing to loose by being honest at this point.