Here's the thing ... all these recharge kits miss one big point. Before you charge the system, you want to test it for leaks under pressure. Then you need to draw it down to vacuum. Only then do you add the oil and Freon charge. If you don't, a portion of the volume will be useless damp air. Now not every shop is going to be ready to handle an old car conversion, even if they claim the expertise. And even a quality shop will have it's share of wrench apes and counter monkeys. You're best off not volunteering an opinion. If you don't tell them what you know, if they try to sell you blinker fluid, you know to keep shopping. Letting them know you're not a mark might have them singing the right song, but still half assing the job.