OK, grabbed that little dusty thing off of the wall it was nailed to. The servo I used is a JR SM22. I had to space it up off the chassis so that the servo saver would not be below the chassis. It seemed to work fine even though the specs seemed light. Since the car does not weigh much, it did not need to exert much force. I never noticed that it lagged command either. The pinion is missing, but I recall working with 4:1 or 5:1 ratios.
I am going to be real skeptical that you are going to get a "light" to hook up on asphalt. That will be the deal breaker right there. The 3.7v seems to be here to stay until the next big invention. I still say give it a try and prove us wrong.