That's a tough one.Make sure the cat/cats don't need "cleaning" causing a lack of power.Maybe a bit more gear.They did have a bit of torque but it was max at 2400-2600 if IIRC. H.P.was only around 160 at 4400.How about the fresh air inlet set up from a later 150 or a Dakota.That and the gear should be available at the local junk yard.