Where's Tak Ma Doon road? I've heard of that. Is that Kilsyth?
Now realising it could be the road to my golf club where I see people cycling past every weekend!! ha ha
If you decide to take on the Tak (and by all means do, it's a great climb), remember that it's tougher than any of the climbs on the sportive. And be careful at the ford on the northbound descent.
I haven't done the climb up from Denny, but the road from Bannockburn up to Carronbridge would be a pretty good practice climb. Reasonably gentle gradient most of the way up, and then a steeper ramp at the end to tell you how well you paced yourself.