I don't want to take anything away from the Weaver GG1. I only paid $150 for my 4816 and have 6 of the 8 paint schemes Weaver offered. Just missing Amtrak and Conrail. If the price is right, you have a nice brass locomotive that can be upgraded for less than the cost of an equivalent Lionel scale GG1. The single stripe PRR schemes (DGLE, Tuscan, & Silver), Penn Central, Amtrak, and Conrail all had flywheels on the motors.
The only other detail that may or may not matter to you is that Weaver, Williams, and MTH GG1s are 1/2" short of full scale and the drivers are a hair shorter than 1:48. I suspect this was a compromise to take the curves better. Many of the parts are also interchangeable between all three.
The Lionel JLC / Legacy and 3rd Rail GG1s are true 1:48 proportions if that matters but I have found that they both really need 072 curves. My only complaint about the Lionel G is the plastic pantographs as I have not experienced the issue on the side frames with mine.