The three tasks for this one are:
• Complete 5 laps in a Vintage Sport Coupe Division car
• Beat a Rival
• Complete a Race in the 2010 Noble M600
These can be easily be done in Free Play mode by selecting the appropriate car and track for the task! Make note to verify that the task completion popped on the #Forzathon tab (if it hasn't then restart the game or hit up a different task and it should pop).
EDIT: I've added specifics for just this challenge then followed it up with a mix and match for all six challenges to get them all done quicker.
Head to your favourite race track, select the shortest course and set the number of laps to 5 with the Vintage Sport Coupe Division selected and finish the race. Next, head to Single Player > Rivals and select a rival to beat. Once you've beat your rival, head back to your favourite track, select the shortest course with 1 lap and complete the race while driving the 2010 Noble M600.
Six challenge completion with fewest number of races
Of course, you can mix and match tasks to work on all six of this month's challenges at the same time. I've posted what I think is the easiest way to complete them all with the fewest number of races below.
You can finish these tasks in Free Play mode. For starters, hop into an Exotic GT Division car, create a 3 lap race at an Autodrome Nazionale Monza track, and you should be able to finish up three tasks at once: complete 3 laps at Monza, complete a race at Monza, and win a race.
Once you’ve done that, hop in a Vintage Sport Coupe Division car and start a new race on Circuit of Americas (East Route) with 5 laps at night to take care of two more tasks. Finally, hop into the 1973 Ford XB Falcon GT, reduce the number of laps to 3 and you’ll be finished the first set of tasks.
Set up a new race at Mugello Autodromo Internazionale (Club Circuit) and hop into the 1977 Pontiac Firebird Trans AM. Go at least 120mph (193km/h) on the straightaway and that’ll get you both the 120mph in the Trans AM and the 100mph at Mugello (161 km/h) in one shot. After you’ve done this, you can hop into a Sport GT Division car and set up a one lap race on Virginia International Raceway (Patriot is the shortest track) and, taking it easy, make sure you stay on the track to complete that task. Next, head into Single Player > Rivals and pick a rival event. Make sure you beat your rival and you should clear up the second tasks for both “Fingers Crossed” and “To Arms!” after which you’ll have one second tier task to complete.
To complete the final second tier task (complete a race at Yas Marina at night) and finish a final tier task at the same time, start a race at Yas Marina (South Circuit and North Corkscrew are the shortest) at night with enough laps to guarantee a win, hop into a Forza GT Division car and upon winning you should be done “Touring Italy,” scoring yourself the 2013 Audi R8 Coupé V10 plus 5.2 FSI quattro. Of course, you’ll have to win another race at night so stick to the same course and hop into a Hypercar Division car. Winning the race this time should complete both “Spectacular Journey” and “Night Time Driving,” netting you the 2013 Bentley Continental GT Speed and 2000 Plymouth Prowler.
After that, you’ll have a few single races to mop up. Select your favourite short track, set it to one lap and hop into the 2010 Noble M600 or the 1998 Eagle Talon Tsi Turbo. Complete the lap (and the race) and you’ll finish the corresponding challenge. Switch to the other vehicle and repeat the same track/lap and the other challenge should complete for you as well. Completing these challenges will reward you with the Surely You Joust Driver Gear and 2013 Audi R8 Coupé V10 plus 5.2 FSI quattro.
Finally, you’ll have to go online to the Multiplayer section and select Pass The It from Multiplayer Hoppers. Once you’ve completed that event, you’ll have finished up “Fingers Crossed” and snagged the final reward: the 1972 Chrysler VH Valiant Charger R/T E49.