You can use a "trick", Google around and find a manual page, say like this one.
Then, instead of meticulously measuring an actual engine (and Lord help you if you're not using a caliper with a digital readout!), simply capture the image, place it on a frozen layer, and meticulously TRACE it in your CAD program. Don't worry about the actual scale yet, in fact, enlarge the image to get the detail easily.
When that is completed, make your traced image into a block. Carefully measure some known distance (say overall length or perhaps center to center on mounting holes) and compute a required scaling value. Then insert your block at the scaled size to make it 1:1, explode the block, and create a new 1:1 scaled block.
Now, pretend that you actually made the drawing.. ;->
L.
"I saw a tree fall in the woods, and I didn't hear it." -Steven Wright