I want to swop a 904 transmission for a A500. What modifications will be required to install the A500?

Is the A500 an electronic transmission?

 

Early 90's are non electric. You can use some pressure switches to activate the overdrive. Will need to shorten the drive shaft and change the trans mount to the A500 style

 

Check out my post "Big time swap" some good tips in there
The a 500 should be none electric the A. E .series have a electric selonoid for overdrive the other issues will be size the overdrive tranies are longer and wider at the tail shaft.
which meens the trany mount , cross member and drve shaft/ trani tunnel will also need modifications .
I did the swap with no major shop or tools yoi will need metel fab equipment though ...welder cuter and the such.
it was worth it for myself best swap I have done to date.