There are woodcarvers, and then there’s Gary Tatman, of Glen Burnie, Maryland. Gary explains his incredible work on Hemmings Auto Blog:
You’re correct in your assumptions- these carvings start out as a block. I use the Internet motorsports archives to obtain enough photos of the project car for detailed areas such as interiors, engine compartments, suspensions etc. Once all data and photos are assembled, a ratio has to be determined for scaling (in reference to actual body size). Then all areas can be measured and used in the ratio to determine the actual size of the pieces. Once this is accomplished, the design needs to be drawn on the block, for references while shaping takes place.