There's a notch on the forwardmost cam bearing tower. It's almost an inch away so alignment is only as good as your eyesight.

[edit] Okay, maybe not an inch away. There's a good picture in this thread -

http://www.peachparts.com/shopforum/showthread.php?t=231159

[edit] And a raised pointer rather than a notch.

Sixto
87 300D