The idea that the concrete blocks are necessary to properly stress the wing structure is a popular myth (even heard from time to time within Boeing). But it is just that - a myth. The engines are normally the last thing installed before the aircraft rolls out the door. The flight loads the wing is designed for are far, far greater than the static weight of an engine hanging off the strut (and yes Ken, we've always called them struts - in fact the now Propulsion Systems Division was once known as "Power Pack and Strut".
As noted, I occasionally saw the nose gear chained to concrete blocks or to the ground when the concrete block engines were not readily available.
Once, many years ago, we were taxing to the far south end of Paine Field preparing for takeoff for a flight test. I saw a brand new 747-400 parked in a remote corner of the field that looked really strange, but in a good way. It took me a second to figure out why - the wing was complete clean. No engines, no struts, not even any pylons
. I have to admit that hanging all that engine hardware on the wing destroys the clean lines of the wing. There were also chains tying the nose gear to a large block of concrete. Come to find out, Rolls had gotten behind producing RB211-524 engines for the 747-400. One operator decided they didn't need their new 747 right away so the pushed the engineless aircraft to a far corner of the field for six months while Rolls production was able to catch back up.