Are all big block 727 valve bodies the same? Specifically, would a 1970 440 six pack 727 use the same factory installed valve body as other big block 727's of the same era?

I think the valve body are pretty much the same for a model year?
Depending on the neutral safety switch used, the shift/rooster comb is different, and later year versions had the part throttle kickdown addition.
I don't know if the internal calibration is different, but installing a shift kit would change that anyway.

The reason I ask is that I don't like the way the 727 in my 440+6 GTX shifts. It shifts unlike any stock 727's I have had in the past so I suspect maybe the valve body was changed sometime in the past. I don't know the history of the trans but it is the original numbers trans to the car. I would like to have the car shift like a stock trans would as the car is otherwise all stock anyway. I have a 70 727 trans from a full size Chrysler and thought if they used the same valve body I might swap them with each other.

How does the shifting differ from your previous cars?

When I get the car moving from a standstill in drive and under normal acceleration, it shifts very quickly from first to second gear and there is kind of a down surge that makes you lurch forward. Of all the Mopars I have had with 727's this is the only one that has done this. The shift from second to third is normal. Maybe something else is causing this but my first thought was the valve body.

My A-body did that. I believe the 727 in it was a '72 vintage. It shifted too fast through all gears. It did not shift crisply into second gear and also had what seemed to be a small amount of drag when shifting at full throttle from first to second.

I put a shift kit in it and it helped the shifts become more positive but as I recall it did not do a whole lot for extending out the time between shifts.

I have a '74 Trailduster and it up shifts and downshifts far better than earlier types I have had. I have heard that right around that year (74) Chrysler revised their throttle bodies to work better.

The 70 throttle body will probably behave the same way the current one in your GTX is behaving. I would look for one out of a '74 and later piece or find out how to make the old ones work better.

The road speed at which the trans shifts and the firmness of the shift is controlled in part by the linkage adjustment.