Already looks good to me! I didn't realise FM4 track conversions were possible. There are some rich pickings there.
Forza Motorsport 4 Tracks and Circuits
Camino Viejo de Montserrat
In-game circuit variations: Full Circuit, Full Circuit Reverse, Extreme Circuit, Short Circuit, Short Circuit Reverse, Mini Circuit, Mini Circuit Reverse
Bernese Alps
In-game circuit variations: Festival Circuit, Festival Circuit Reverse, Stadtplatz, Stadtplatz Reverse, Club Circuit, Club Circuit Reverse
Fujimi Kaido
In-game circuit variations: Full Circuit, Stage B, Stage A Reverse, Stage D Reverse, New Hillclimb, Full Circuit Reverse, Stage C, Stage B Reverse, Old Hill Climb, New Downhill, Stage A, Stage D, Stage C Reverse, Old Downhill
Hockenheimring
In-game circuit variations: Full Circuit, Drag 1/4 Mile, National Circuit, Short Circuit
Iberian International Circuit
In-game circuit variations: Full Circuit, Full Circuit Reverse, Short Circuit, Short Circuit Reverse, Mini Circuit, Mini Circuit Reverse
Indianapolis Motor Speedway
In-game circuit variations: Long Course, Drag 1/4-mile, Indy Racing League Circuit, NASCAR Circuit.
Ladera Test Track
In-game circuit variations: Full Circuit, Full Circuit Reverse, Short Circuit, Short Circuit Reverse, Mini Circuit, Mini Circuit Reverse
Maple Valley Raceway
In-game circuit variations: Full Circuit, Short Circuit, Full Circuit Reverse, Short Circuit Reverse
Mugello Autodromo Internazionale
In-game circuit variations: Full Circuit, Club Circuit
Nurburgring Grand Prix Circuit
In-game circuit variations: Full Circuit, Short Circuit
Rally di Positano
In-game circuit variations: Full Circuit, Full Circuit Reverse
Road Atlanta
In-game circuit variations: Full Circuit, Club Circuit
Sebring International Raceway
In-game circuit variations: Full Circuit, Club Circuit, Short Circuit
Silverstone Racing Circuit
In-game circuit variations: Silverstone Grand Prix Circuit, Silverstone International Circuit, Silverstone National Circuit
Suzuka Circuit
In-game circuit variations: Full Circuit, West Circuit, East Circuit
TopGear Test Track
In-game circuit variations: Full Circuit, West Circuit, West Circuit Reverse, Drag Mile, Outer Loop, Outer Loop Reverse, Drag 1/4 Mile, East Circuit, East Circuit Reverse, Drag 1/2 Mile
Tsukuba Circuit
In-game circuit variations: Full Circuit, Short Circuit
Twin Ring Motegi
In-game circuit variations: Full Circuit, East Circuit, West Circuit, Super Speedway