I'm not sure how much of the relevant detail carries over for production at HO scale, but both Kohs and Fine Art Models had fairly detailed discussion of the details of their respective versions. Some of these (e.g. the rolled edge under the shell) might have been things to consider in newer versions.
I suspect I'm still waiting for accurate quill-drive details in the drivers. And hoping for an 'aged' sound set (including that wonderful worn-gear-tooth howl some engines had in the mid-Seventies, in common with the last of the NYC subway R1-series cars in service) to go with 'weathered' versions.
Several years ago MTH sued BLI. As part of the settlement ( as I recall) BLI had to give MTH their GG1 tooling. There is not a lot on a G that could be improved due to the streamlined body. The pilot on the early models is about it in my opinion
Broadway Limited Imports' new GG1 (HO) release promises new tooling. Does anyone know what's different, other than the announced flat pilot? I've was briefly able to compare the new release with the original (2003?) made in Korea version, and noted (a) crisper detail in the undercarriage; (b) finer/skinnier material in the pantograph, at the cost of making absent or nearly invisible some of the details visible in the earlier version; (c) more accuracy in ventilation grids on the side (specifically, flat panels partially covering the vents where the broad paint stripe goes over it). I'm wondering what else is different in the new tooling. Thanks.