I thought I saw a Chevy 292 straight-six advertised somewhere on this website. These have lots of torque and would replace the original straight-six without any V-8 'width' problems. For a tranny, I'd suggest a '89 or so (pre-computer) Chevy 700R4 4-speed auto overdrive unit. This would allow you to keep an older higher-geared rear axle.
Regards,
Apache Kid
