The VF is not a ducted fan engine, VFDF is. VF is a FIRE for pattern planes, like a small 1.40 RX.
Point is moot however, as VF is long discontinued.

Do you need it to be rear exhaust? If side exhaust is OK, Henry Nelson makes a .65 that is very strong running. Call him, he can tell you all about it. I love mine!

Jett also makes engines in both FIRE and FISE configurations that are available tuned for low rev torque.

Good luck!