Does your 400 look like this ? Starter on the driver side oil filter on the passenger side. The oposite of the chevy engine. If so its tha American engine and will not bolt up to a small block trany. different bolt patern.
If you change out to a rear whl. drive Olds tranny[turbo 350 BOP pattern] it will fit with a few mods. Need Pontiac flex plate, mounts etc & poss. frt. yoke on D/shaft & of course new exhaust system at the frt.!!!!!
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Some times I wake up GRUMPY, but today I let her sleep in !!!!!!!!BLACKSTOCK Ont.