Last June I paid a small fortune to go from Kathmandu > Everest Base Camp > Lhasa and back. It was all go up until 2 weeks before departure, then the route changed, still crossing the border but the NW route. Then 3 days before departure it changed again... this time they said they couldn't cross the border, but had arranged flights from Kathmandu to Lhasa.
Ended up riding PoS Yamaha 250's, and an uncomfortable Benelli from Lhasa down to Everest and back. Bike's had parts falling off the first 500km.
The views were amazing, but I paid to cross the Nepal/Tibet border, and see the change of climate/scenery on a Royal Enfield, not from 33,000ft above.
The tour operator did what they could, and didn't collect me the first day, which made me pretty pissed.
I decided to go with a tour operator bcos I had a lot of conflicting information from local agents, and most were unresponsive.
If it was me, I would ask around Pokhara more (it's pretty big and touristy), internet isn't that much use bcos web pages can be totally wrong/out of date/out of business.
You may need to hire a guide... remember roads come and go, and the locals think your stupid tourist with nfi. I hired one in Peru who was invaluable.
I reckon Kathmandu would be the same situation as Pokhara, when we arrived back there was one of the tour group who wanted to take an Enfield on a day trip and his only option was with a guide, and that was 1 bike, not 6.
Here's some pic spam...