Thank you for all the kind comments.
Sorry, normally my report thingies are more verbose. Here is the route:

Basically we cycled the normal landrover track/walkers path NE along to Airgiod Bheinn. Then ascended it's very, very steep slopes with the bikes on our backs. Cycled along and up to Carn nan Gabhar. Left the bikes for the last 20m or so.
From there it was an excellent, very fast, not-too-technical descent down to the bealach at NN958727. It was about 3pm and we were becoming conscious of the limited hours of sun remaining. So, we ramped up the pace and blasted up to the summit of Braigh Coire Chruinn-bhalgain with the bikes on our back. The second Munro of the day.
The descent back down to the start of the final ascent was really good fun. Very fast and very technical. There's no obvious line for much of it so we enjoyed taking our own lines, jumping off any rocks in our path, and generally being "gnarly" as the kids would say. Time for a sandwich before commencing the last climb for the day starting at NN938714. We met a dog, who was very friendly, and a few walkers who were not friendly at all. Here is a very grainy photo my friend took on his phone of us reaching the bottom:

The final ascent starts with a short section of bike-carrying, followed by a long, moderately steep cycle to the final summit - Carn Liath.
By this time the sun was starting to set, casting a beautiful orange glow over everything. We spent some time at the summit soaking up it's rays, enjoying the atmosphere and posing for photies.
The final descent was pretty wild. Probably the most technical thing I've ever ridden (Ben Lomond comes a close second).
We all crashed a load of times, but wear elbow and knee pads so it's not a problem. All part of the fun. There was a section where we kept overtaking each other then crashing - great big smiles on our faces and laughter in the air
The walking/biking ratio was about 70/30 which is poor, but we expected that. Walking up mountains with a bike isn't too bad once you're used to it. My bike, plus water, clothing, spares, tools and other gear probably totals about 30kg. I'm sure many people carry more weight when camping.
I wouldn't recommend anyone do this route on a bike unless you're very experienced walking with a bike on your back and at descending steep technical terrain.
If anyone is interested in more bikey-Munro routes let me know and I'll post some. Some are 100% possible on a bike. A climb up to Mullach Clach a'Bhlair, then along to Sgor Gaoith before descending via Carn Ban Mor makes an excellent day out and isn't too technical.