Safe to use Wheel Adapters 5 on 4" to 4.5"?

So, I'm converting to disc brakes up front (65 Plymouth Valiant Signet convertible) so that takes care of the front. The rear I had planned to use high quality billet 1" adapters. I ordered 15x7 front/15x8 rear US Mag U107 rims with 215/65/15 front/ 235/60/15 rear Cooper Cobra tires from Discount Tire. I told them that I intended to use rear adapters, even showing them to them, when I ordered and paid for the package. Today they tell me they are in but, not only won't they mount them, they would not even sell the rear ones to me knowing my intentions! They said they have a new policy about adapters but could mount to spacers. So, I can cancel and order from someone who will mount to adapters or I can explore other ways to get a 5x4.5 pattern in the rear. Any experience, ideas or advice out there? Thanks in advance...