G'day gml,
A very fitting job for her! And it's good to see them in active use.
Is it going to support a museum collection?
The drive is well suited to use as an aircraft tug as the clutch allows a very gentle action- which is what is needed. Perhaps a lower gearing ratio would be ideal to improve torque and slow the forward speed. Not sure how you'd do that easily though. Only way is to try it out.
Are they small aircraft? I ask because one of the other problems with adapting OPE to this kind of application is weight. The adapted mowers aren't heavy enough. One solution is to sling weight from the deck mountings.
Does this mean you're in the market for another project? If so I might be selling

Cheers,