Browning did not make the Model 70, Winchester did. Also, the serial number is not a valid Browning serial number for a 7mm Magnum rifle. Please doublecheck your information.
The G prefix to your serial number shows that it is a model 70 Winchester rifle.It should say this on the barrel of your rifle.
The 7mm Ultra Mag is a Remington cartridge. THE model 70 is a Winchester rifle. Winchester does not chamber the Model 70 For the 7mm Rem. Ultra Mag cartridge.
Proofhouse.com has Winchester sn data
Price of a Winchester model 70 pre 64 in 7mm mag
The year of manufacture for serial number 801666 is 1965. From the ever popular web site http://armscollectors.com/sn/winlookup.php
The answer to this q? is 1-9"
TRY THE WIN COLLECTORS SITE
250-600 dollars.depending on overall condition.