I wired a blitter to my upgraded 520 using veroboard and ribbon cable. Took all night, and I only needed to do that because the socket I had was the wrong footprint for the motherboard. It was running a pre 1.4 TOS, and recognised the blitter, you could turn it on /off in the desktop settings menu.
So, not to dispute what wongck said, but my own experience was wire and forget, no additional boards needed.
Too many retro computers here: 1040STfm, Mega4, Ultrasatanx2 , Amiga A500, A500+ and A1200, Acorn Atom x2, BBC Micro, Electron, Spectrum 48k x2, +48, +128k, QL, Oric Atmos, ZX81, Memotech MTX512, Amstrad 6128 x2..