Not-sure why you don't buy the correct shocks? I suspect you've found a pair on CL or facebook market, and are hot-to-trot on the purchase. A starting point would be to find-out the weight of the H-D they are supposed to fit, and compare it to the ~600 lbs weight of a Gen I. Any significant difference, and you'll need to buy a proper set of springs for your shocks. There-goes your savings! There are different bushings you can get for the mounting eyelets, having different I.D.'s. Another consideration is the width of the H-D eyelet compared to that of the V-Max. A lack of compatibility here could cause a serious point of weakness in the mounting, not something you want to-have happen, your *** collapsing onto a spinning tire because a shock mounting stud or a shock eyelet broke. That's an extreme example, but remember that first b&w album cover art by Jimmy Page, Robert Plant, John Paul Jones, and Robert Bonham?
Where are you located? Someone may have a set they're looking to sell, properly-sized.