71 Duster 340 Inviolet V-24 How Rare??

Whats the best way to go on the underside. Matched Paint, black or undercoat?
This looks to be a factory undercoat car but want to do whats best for retaining the value. Sending it to the blaster in about 2-3 weeks. They provide an undercoat service when the car its done blasting. Just don't know if it would be better to color match it. Any Opinions on this? Thanks