By a 70's convertible I take you mean a 124 Spider. I have been looking at buying one myself, and although I do not have a lot of experience of them first hand there is a huge resource for them on-line. If you go to
http://www.fiatmotorclubgb.com and go to their links section you will see many. You can also ask questions on their sometomes usefull forum. Have a look at the cars sections as well. Its the best resource for classic Fiats in the UK. As for the US, there are a number of Owners Clubs and web sites - there are too many tho list!
You then need to decide how "classic" you want to go.
The spider came out in the mid 60's and ran until '85 as far as I can work out.
The original was 1438cc S4 DOHC rising through 1608cc in the early 70's 1756cc from '74 and finally 1995cc from '79. There have been reports of some turbo charged (Volumex) versions in the US but I have never seen one here. There are also not many RHD cars.
From '82 the cars were badged Pininfarina Spder Europa!
Finally there was an Abarth Rallye version with black bonnet but only just over 1000 were made and they were built in '74 so how many remain is unkown,
As you are in the US you will have the pick of the best and widest choice available.
Me - well I want a 2000i in Metallic Blue with a black hood!
Keep in touch, I would like to hear you opinions.
Nige
Fiat Bravo HGT155
Jagaur XJR-S 6.0 V12
http://www.bravo-guide.co.uk THE Fiat Bravo site