Here is an old link to a couple attempts to make this change. Unfortunately the pictures have expired and there is no indication if either attempt was successful.
You have to consider this conversion may require precision work. Consider rainwater leakage and unwanted air/wind noise from any gaps.
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/349630/1.html


"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."