My EJ22 is a SOHC motor. Not sure if or how much wider the DOHC motor is. The drivetrain is the stock drivetrain for now. I just used an adapter plate to mate them. The 1981 GL brats had the dual range 4-speed transmission so I was able to do that. Your brat should have the single range transmission which is set up different than mine. When my transmission stops working I am going to put in an EJ AWD or an RX awd transmission. I did a little write up on my brat on the old forum, so the pictures are not there. Here is the link:
http://www.ultimatesubaru.org/forum/showthread.php?t=88632&highlight=1981+brat