The left side engine mount bracket for Twin Cam has a part number different from the pushrod engine bracket. At first I thought the only physical difference is one additional hole in front for a countersunk screw passing forward through the timing cover flange. However, the lower hole in the front flange is also in different location, slightly farther outboard.

Twin Cam Left Engine Mount --- Pushrod Engine Left Engine Mount
The third bolt on Twin Cam LH engine mount (below)

John Hopwood has provided this template to make a Twin Cam left engine mount bracket. Or you might start with a pushrod engine bracket, weld the two front holes shut, and drill and countersink three new holes.

At time of this posting, Jim Alcorn at Auto Vintagery in La Jolla, California had a few of these parts available.

For more information on how to modify a standard bracket to fit a pushrod engine, see part number page AHH5703.htm.