My understanding after re-reading your post, your intentions are to carry oversize lumber. I am not sure if any of the luggage racks were intended for such loads and would carefully search for information regarding such use. You may want to check with a specialty truck store that caters to construction/tradesmen. I think your idea of a gutter mounted rack is a better idea than an original bolted through the roof mount. If you check ebay, try searching for: luggage rack, roof carrier, roof rack etc. also there are later model racks, both foreign and domestic that might adapt to your roof, so take measurements and compare. Good luck!
This is one style that was available in the 50's and 60's
http://sfbay.craigslist.org/nby/pts/545521611.html