Realtime emulation

27c512

For the top board chip you can use any 8 bit emulator. I recommend the Moates Ostrich due to native TunerPro support.

87c257

Here it is a little more complex. The only emulator I know of that natively supports the 87c257 chip is the OLS300.
The 87c257 is essentially a 27c256 with a built-in tri-state latch.
You can still use the Ostrich, but you will need an adapter with a HCT373 latch to provide the latching functionality for the multiplexed bus.

At the current point in time, your best bet, is to order the "SBEC Adapter 3" here:
https://oshpark.com/profiles/BoostButton/page/2
Then buy a HCT373 latch, some 2.54mm headers, a socket and solder it all together. The resistor can be omitted.

There is one known issue with the Ostrich. You will need to have the Ostrich that is emulating the 87c257 powered when switching on the ECU power, otherwise the ECU will not boot the first time.

The Future

Due to the advances in microcontrollers, it is possible to create much smaller emulators, that can fit completely into the ECU and communicate using bluetooth.
If anyone reading this works in embedded design and wishes to help - please do let me know.