FWIW from my reference file comments on DA50
Width for the center of the standoffs is 3 1/8 inches
Height is 2 5/8 inches
The diameter of the standoffs at the firewall is 11/16"
The standoffs are 2 1/2" long
The engine is 3 3/4 inches long for a total length from firewall to hub of 6 1/4 inches
The standoff at the firewall does take a standard thread 1/4" bolt
Hope this helps and matches the figures on DA's website. I took it right off a model in progress
The end 'footprints' are the largest dia. The balance of standoff is turned down to about 60% of that diameter.