Re: cruiser with a straight bar ?
most bicycle frames are too short lengthwise.
and especially if you wish to use the swept-back cruiser styled bars.
IMO it would be fine to use a suitable rear section, and fab your own tubes from the seatpost forward to a neck appropriate for the front forks of your choice.
IMO if lengths were cut and fitted there would only be an hour's welding labor involved, if you do not have that equipment.
IMO best to purchase new tube because salvaged bike frame pieces are always too short. the simple bends required could be accomplished cold with a 8lb hand sledge and blocks of wood. a $20 hf grinder should be sufficient for the task of fitting.
My goal is cheap, reliable, personal transport, below the tax collector radar. Fun counts for a lot!