Whilst building the RV-3 fuselage, it suddenly struck me there was a discontinuity in major longerons in the lower fuselage between the main and rear wing spars...
It made me go back to the plans and check I had not omitted something... and then realised, no I had not, the "load" path is provided by the wing structure itself.
If you do choose to run the engine without the wings bolted on, think through how the "box" rigidity of the fuselage (in twist) is compromised by no wing box, and also the straight line path from engne to tail (i.e. tying the tailwheel down does not really help since there is a structure "gap" between the wing spars). Trying to quantify these elements is nigh on impossible - the only people qualifed to answer are Vans, and we know their opinion on the matter
Andy