If you need more gearing than tranny swapping will do alone...then maybe look into if there is a slightly taller but skinnier tire that will fit the metro.
I thought I spotted a turbo in on of the earlier pics. When you get around to putting it on it should help out by shoving more air into the motor to compensate for the imbalance between air and fuel right now (black smoke). An external adjustable wastegate will help keep you from overboosting. DSM and honda dudes use them frequently. You may need to put head studs in the thing to keep the head gasket in place if it was not designed for a turbo to begin with.
Cool project, keep us updated when you can.
