I think you'd be fine with driving with your old plates as long as you follow the rules.
As far as the issue, it does sound like a typical MAF issue. Try swapping the one from your car into his and see if that fixes the issue. If it does, then there you go.
oh and FYI The lifters in SOHC's don't tick typically like the DOHC does.. and you're 99 has the same lifters that mine and his do
it's an SOHC!
