hey barbs - You should buy the book "Corvette Chassis Restoration Guide" by Joseph Tripoli. There is an UNBELIEVABLE amount of chassis, spring, brake, vin, information, plus tons of photos that will help you. There is even a section that shows you what the letter/numbers should look like. From the Chassis stencil chart, 1969 shows 3973880-xx. The xx is the AO Smith production number and you will need to calculate that. you will also need to calculate your date and that needs to be added also on the second line.
ISBN for the book is 0-9624817-0-x
Good luck with your resto