Boeing has proposed funding its acquisition of partsmaker Spirit AeroSystems with stock rather than cash, according to people familiar with the matter, a last-minute twist in deal talks that comes as the jet maker burns through more than $1 billion a month. Boeing and Spirit, a jet fuselage maker it split off two decades ago, were closing in on an all-cash deal this weekend when Boeing switched to an offer consisting largely of company stock. The two sides discussed a deal that would have had Boeing paying more than $4 billion for the two-thirds of Spirit’s business that supplies it with parts.