I did it about a month ago. Got a full copy of my original invoice!
Pretty sure they can do it from VIN only, they do ask for the tag details as well but I don't think it made much difference to my order as all their emails kept referring to the VIN number. They only charge you if they find the invoice I think, no charge if no discovery (double check that, but I'm sure that's what I read) so no harm in trying.
In all honesty though, you can probably work out most of the tag details. The VIN will tell you which plant, then you can work out which cowl tag type. Hopefully you know what color it was originally? Lots of info on mine were on other labels as well (like manufactured date on a sticker on the drivers door etc.)
This link will help you decode your VIN:
http://www.nastyz28.com/camaro/camaro79.php
This link will help you 'build' your tag specs
http://www.chevy-camaro.com/chevy-camar ... e-1979.asp
This is a site to get replica tags
http://www.trimtags.com/
Then go to GM Heritage and get a copy of the invoice!
Then you can go one better and go here to get a copy of your dealer window sticker here:
https://www.window-sticker.com/
Only thing I can't find, is any way to get a copy of your build sheet. I found fragments of mine under the drivers seat, but only managed to piece together about 30% of it.......
The cowl tags pretty much only spec the following
Every time: GM, Camaro, Hardtop, Bucket Seats
Then either Sport Coupe / RS / Z28 are all the same with Berlinetta different
Manufacture plant (get from the VIN as well) either Norwood or Van Nuys
Interior Trim Code (looks like yours was Tan Vinyl Standard, 62R, originally)
Body Colour - Do you know if yours was originally Black?
Paint Type (nearly always W for Water)
Dash Panel colour (looks like yours was Tan, T, orginaly)
T-Top or not (looks like yours wasn't so ---)
Power Brakes (should be obvious, vac hose going to booster or not?)
Accessory Code (only way to tell if 'genuine' Z28, option 8 from Van Nuys / LA, other than looking at car specs)
Power Windows (should be obvious!)
Plant Batch Code (where it went down the track, not linked to VIN so hard to work out but also fairly meaningless)
The only other important bit is build date, which you may be able to find on the door sticker as well. Or the build sheet if you can find it under the seat / on the tank......
Hope that helps!