Fascinating film footage. Thanks, Ivor.
The venue is Ahoy Hall, a large indoor sporting arena in Rotterdam, built in 1950, expanded in 1970, and expanded again in 1998. It's still in regular use for major rock concerts and sporting events. During this live performance and recording (3 July 1954), a sound-absorbing floor covering was deployed and tram service was interrupted in the area to avoid interfering with the performance. Programs were printed on special soft paper to cut down on noise from that source. At the time, the hall seating capacity was 8,500 and the concert was sold out.
As to the organ, it certainly doesn't look portable to me. I'd guess it was a permanent part of the arena, at least in the period from 1950 until 1970.
This is the same performance issued on Philips LPs, and now on Scribendum CDs. Scribendum say the date was 3 July 1954. The timings for the two movements are 25:48 and 56:06. The transfer is just okay, but better than the one given to the accompanying Wyn Morris NPO M10. I'm told there is a much better transfer available on the Rotterdam Philharmonic's own label, but I can't vouch for that. The performance itself could best be described as scrappy but enthusiastic. No problem hearing the children here!
James