Heston 'runway' length
That's probably about right but it was not the usable 'runway' length. In 1934, ten cubic yards of chalk were put down to create a white dotted line, indicating the approved take off and landing axis over the grass. That axis, still shown in use in the 1945 aerial photo I mentioned (crossing North Hyde Lane at the Fern Lane corner), by 1939 when an initial easterly extension had been added, provided an Air Ministry designated 1000 yards/3000 feet 'runway' plus height clearance buffer zones at either end - e.g., to clear the house the Ju88 hit.
Scaled up to also include the further easterly extension shown in the 1945 photo, and even assuming that the height clearance operating limit moved eastwards to the same extent, then the final usable length (except in extremis - e.g., Gen Curtis LeMay in a hurry in a B17!) was somewhere between the 3,850 feet I previously estimated, and say 4,000 feet absolute maximum. About 300-350 feet overrun/height clearance buffer at each end, would have been quite normal for aircraft, often with low initial climb rates in those days, operating in a built up area.
The 1945 aerial photo clearly shows a well worn touch down area on the grass surface at the western end of the 'runway' beginning almost exactly 300 feet east of the perimeter track, and extending right across to about 700 feet onto the grass. A 1935 photograph in Tim Sherwood's "Coming in to Land" appears to also show a threshold marker line at right angles to the dotted line 'runway' axis, at about 300 feet in from the peri track.
All academic though really, as the point was that Heston was never a bomber base, and once Blenheims, Whitleys and Wellingtons left the main bomber force inventory, it never could have been. In particular, Heston was not "always busy with Flying Fortresses taking off and landing".