If you can run to a drum mower get one, they are better at there job, easier to maintain and spares more easily available. If you go with the finger mower forget the early ones and get a later rigid framed model, they are now old technology, but were very successful in their day, and can still do the job.
Of course just to confuse the issue there were disc mowers which were ideally suited to the 135, ( a 5'6" drum mower being near the limit of what a 135 can handle) but they seem to really rare these days.
If buying a drum I wouldn't risk buying one without seeing it operating, they spin a massive rpm and need to be in balance, they could be uneconomical to repair if damaged. Hence my earlier suggestion of buying new.
The dilemmas of life !
Cheers stu