Enabling ROM while the CPU's driving was somewhat common on the A2, and the 74XX chips involved generally were tough enough not to care. We know that Apple internally used writes to various system ROM addresses to cause an ICE to log specific events.

Regarding the handshaking, the Apple parallel card doesn't handshake properly with the AP2000. I spent a significant amount of time fighting with it and couldn't get it to work reliably. Part of it was MAME time slicing: you write a character to the printer, and the printer's CPU doesn't get a chance to latch the character and drive the busy line before the next time the 6502 goes to write something, but there was more to it than that.