The HKS VPC is by far the easiest.
Plug in a GCC, and tune it from the dash.
Wire in an Apex S-AFC (Apex has this info on their site),
and have even more tuning capability.
No Lap-top needed.
The VPC ROM has all the base 7M info in it.
ROMs available for stock, or 550cc injectors.
I have seen other custom ROMs.
Even if you can't find the correct harness,
several people do up direct wire harnesses
(a whole whopping 5 wires).
Proven track record (they have been around since the late '90s).
And for a really nice one, expect to pay about $500-600.
There are several up on eBay right now.
And the people selling them, usually have the different ROMS.