If your heart is set on having a Resto-Mod with a top that goes down, you're going to build a rare vehicle. Convertible muscle cars were low-production items in the '60s and '70s. Fast take off and fabric tops didn't go well together. However, Detroit did build open-air muscle machines in relatively small numbers. You'll probably find more Mustang, Camaro and Chevelle convertibles around today than you will 'Cudas or Cougars. Survival rates tend to directly follow the original sales figures. If you are lucky enough to find one, building a convertible into a Resto-Mod is going to increase the difficulty and cost of your restoration.
Muscle car convertibles are rare. If you want one, you may have to start with a car that needs just about everything restored, including the convertible top.
There are four main areas of extra attention that a ragtop restification will require:
Convertible top frames are subject to a lot of ordinary abuse as they do their job. Broken nuts and bolts, rivets, screws and grommets are common. Bushing wear out from years of raising and lowering the top. Paint on the bows can easily get scratched, permitting oxidation to begin. The bows themselves can be damaged because the wear and tear on other parts throws the geometry off.
Top frame repair kits are available for some popular muscle cars. These provide every piece needed to replace all of the old hardware with new parts. Suppliers of multi-make automotive hardware such as Restoration Specialties & Supply, Inc. (www.restorationspecialties.com) maybe able to help get the parts you need if there's no pre-packaged kit for your car. The hardware from a still-assembled top frame can often be replaced a piece at a time, but most builders will want to disassemble the frame to paint it and replace all hardware at once.
Even though Jim Mokwa had a pretty good top frame, it had rivets that needed replacement and the fabric top was badly in need of replacement.
When you take a frame apart, it will involve drilling out rivets, as well as removing nuts and washers from bolts. Some of the "bolts" may actually be special pivots—sometimes multi-diameter—that are designed to go through several different size holes in different pieces. These may or may not be threaded at the end. If you remove a pivot or fastener and the hole that it went through is egg-shaped, its roundness will have to be renewed by replacing the part, welding and re-drilling the hole or using some kind of bushing. An egg-shaped hole will throw off the entire geometry of the top and cause problems.
Many restorers rush to paint convertible top frames flat black or some neutral color like gray or beige. However, classic car collectors have documented many cases where the OEM automakers color matched the convertible top frame with the color of the top fabric. While color coordinated convertibles may have been out of vogue by the time the muscle car era arrived, the coordinated combos really looked cool and there's no reason why you can't revive the use of color when you build your Resto-Mod. After all, with such cars, looks count more than OEM correctness. That's why you see white-topped cars with white bows taking home trophies. Chrome- or copper-plated bows might not look bad either.
GTO's original top frame was cleaned, painted and rebuilt. Reproductions of the chrome plated top latches are available for '69 GTOs.
Start disassembling your convertible top frame by removing all of the hardware that can be removed using only simple hand tools. Don't remove any original rivets or spot welds until later. You'll probably have well over a dozen parts like various bows, the scissor assemblies and two side frames. Take digital photos as you disassemble. A great way to organize smaller parts and fasteners as they come off is to get a piece of cardboard, drill or poke holes in it and put the items removed into the holes. Put re-assembly notes right on the cardboard. Save any of the old parts that can either be reused or used to make copies.
Clean paint off the old pieces in your media blasting cabinet or take them to a commercial blaster. As you know, blasting will not remove rust. It can be dealt with the same ways you took care of rust while fixing the body. Then prime, sand and paint the bows like you did your body panels. Considering the wear and tear these parts might be subjected to, you may want to replace the painting step with application of a powder coat. You can hire this job out to a powder coating shop or buy a home powder coating kit from Eastwood Tool or Harbor Freight.
In your spare time, search in hobby publications or on the Internet to see if you can come up with a convertible top manual or complete factory assembly manual (including top parts) for your car. It will be a big help during re-assembly.