There is one size 1954 3600 box (Chevrolet 3/4 ton in USA). It is not a long box; it is a 3600 box, which is longer than the 3100 box and shorter than the 3800 box. I am not sure about Canadian Chevrolet trucks having long/short boxes on 1/2 tons and/or on 3/4 tons.
1954 USA GMCs had a 1/2 ton short box and a 1/2 ton long box. I think the 3/4 ton GMCs had one-size bed (the same length as the 1/2 ton long bed).
"Are the running boards bolted onto the front fenders as well as the back fenders?" Sorry about my terse "no" answer, but it correctly answered your question.
Was/is your running board connected to the front fender?
