I think I mighta figured it out. This is what the NADA classic value guide sez about a '70 300 with the options shown:
[TABLE="class: tbl-pricing used-pricing"]
[TR]
[TH][/TH]
[TH="class: help"]Original
MSRP
[/TH]
[TH="class: help"]Low
Retail
[/TH]
[TH="class: help"]Average
Retail
[/TH]
[TH="class: help"]High
Retail
[/TH]
[/TR]
[TR]
[TD]Base Price
[/TD]
[TD]$4,580
[/TD]
[TD]$9,000
[/TD]
[TD]$16,400
[/TD]
[TD]$23,700
[/TD]
[/TR]
[TR]
[TD="colspan: 5"]Options:
(edit options)
[/TD]
[/TR]
[TR="class: option-row"]
[TD]ADD-300 440/375 HP V8 ENG
[/TD]
[TD][/TD]
[TD]10%
[/TD]
[TD]10%
[/TD]
[TD]10%
[/TD]
[/TR]
[TR="class: option-row"]
[TD]ADD-FACTORY AIR CONDITIONING
[/TD]
[TD][/TD]
[TD]10%
[/TD]
[TD]10%
[/TD]
[TD]10%
[/TD]
[/TR]
[TR="class: tbl-pricing-total"]
[TD]TOTAL PRICE:
[/TD]
[TD]$4,580
[/TD]
[TD]$10,800
[/TD]
[TD]$19,680
[/TD]
[TD]$28,440
[/TD]
[/TR]
[/TABLE]
Looks like the seller thinks that car should go for "High Retail."
.