I've tried to extract some models from model1/2 before. Main technical difficulties are:
1. Most models are stored as many small parts. The way how those parts are orgnized requires lots of time to reverse-engineering. More over, the ways of orgnization may be different from game to game, even with the same kind of hardware;
2. Color and texture data are stored seperately, and pointers linking color/material/texture/polygon data are also scattered here and there, sometimes mixed with program code;
3. Most of those 1990's 3D hardware used z-sort, instead of z-buffer. When extracted them to a modern 3D rendering engine, one may experience some unconfortable visual effect. There were also many 'tricks' when using z-sort, the head-light on the subway train in vcop2, for example.