Don't do it!!!
Yeah, I agree. The Toaster 2000 was made for the Amiga 2000 and the Toaster 4000 for the Amiga 4000 and the AGA chipset. A Toaster 4000 in an Amiga 2000 is ok but it doesn't work the other way round. Not very well anyway and not without cutting pieces of metal from the chassis of your A4000.