i installed a home made jobbie on my M35 today, made a fairly large difference IMO. its nice and smooth, idles well and maybe, only MAYBE, shifts gears faster. im driving down the coast tonight so we will sew how true that is.
not bad for $20 worth of parts, and i didnt even do the gearbox, just the block and manifold. i might ground out the chassis and rough up the factory ground points so it makes better contact