rhm -
wrt to converting your 49D chainset to hex head c/w bolts. the bolt holes for the allen version are larger than for the hex version so some creative adapting would be required. do not know how easily doable this is or if it would merit the candle... one would likely need to washer the bolt head; not a thing of beauty.
wrt tyres. if you elect to build a set of wired-ons two period correct rims would be the weinmann made in belgium w/ferrules and the fiamme yellow label.
afaik there were no box section wired-ons made at this epoch. would recommend against the comparable ambrosio as they are relatively soft/weak.
all best wishes with this as it moveth forward.
