pfft ga16 in a 1200 easy ive put one in my 1200 ute! it wasnt too hard just need access to a gud work shop.first ditch the a15 keep the box mines a 60a then line it up with the ga16 the dowel holes line up and so do three bolt holes,u can make a few more holes work, u have too cut around 12mm of the end of the imput shaft and make a new spigate bush.the hardest part is the fly wheel and starter motor,i used the a12 fly wheel spun a bigger spiget re drilled holes to suit the ga and took 2mm of the front,then lost another 3 kg of meatl for good measures.too get the starter motor too fit i had too chop a bit outa the block ,then but the a series starter motor in a lathe and took 4 mm of the face that bolts too the gear box,in doinig all this it heeps the starter motor fully contacting on the fly wheel teeth. then notch the cross member a little and make new engine mounts and u have an ga16 sitting in a 1200