Larry, I don't know the dateline on the modifications so I suppose it could be after the 250 was introduced but from what I've read it appears to be before the 250. Just another thought.
The 261 idea seems reasonable however but it's a Chevy, not a GMC so back to the factualness of the listing.
Jerry, are you saying the manifolds are not OE GM types? Again, I don't know the 53-54 vette' engines but I always thought it used a more conventional log style intake. So if not GM what are they?
Also...no one has meantioned the selling price. Anybody know?
