I have built three self-made towers! what i did on all three was mount the board with the bottom rf sheild still on!
I cut away any metal that would block airflow to my blizzard 030, magnum 030 and apollo 030 in each case... then i made port extensions with those plugs that use ribbon cables! the only thing that needed a custom cable was the rgb video... everything is on back plates!
I bought angle adaptors for the pcmcia slots! the a1200's led board is perfect for case leds! what i did was remove the original leds and soldered on pin headers... so the case led leads could fit on and be removed easy! the power supplys i have are all AT and i opened them up and soldered an amiga power lead directly to the board (the safest option IMHO)
I bought Power computings keyboard interface which is great! i had to make a hole for the keyboard din plug!
getting parts is easy! go to any Radioparts store or radioshack! or online using Maplins!