The gerber back then was RS-274D. What's in use now is 274
X. I had to learn to convert, but once you have your templates, it's a very quick process to do it by hand in a text editor. After you massage the main aperture list, it can be copy and pasted into most layers' files and they just take just a few seconds each to convert. Plane layers take more time, but if you do it frequently, it's still pretty straight forward. If I haven't done it in a while, it takes me longer since I'm not fresh at it.
I'm still using an old DOS-based CAD which puts out 274D. One reason I stay with it is because I have hundreds of custom component footprints in it which I don't want to have to re-make. Yeah, good CADs come with thousands of footprints, standard, and actually mine came with at least hundreds; but there are always lots more for special parts they don't have, and I re-worked the standard ones anyway for better density.
Years ago, with 274D, when I had complex layers with ground planes, chainsaw lines, text in the planes, shaving pads, etc. I had to do multiple gerber files for a layer, with multiple aperture files, and give very detailed instructions in the readme.txt file. The CAM people tended to mess things up and then call me saying the data were unusable, and I'd have to point out they didn't follow the instructions, that they used the wrong aperture file, etc.. The newer 274X lets you do a lot more, and get all the info for a layer into a single file that the CAM people don't have a chance to mess up. It really made things easier. It's also one of the reasons these board houses now can make small quantities so cheaply. They require a lot less human attention.
For a simple board, you could conceivably lay it out by hand on quadrille paper and take the coordinates and type up a gerber file without any CAD at all. Unless it's super simple though, it might be a question of whether you'd live long enough to finish. There are gerber viewers available to check the output. I use gerbv to double-check my work. gerbv is free.
Edit, 12/1/16: I see there's a free 3D online gerber viewer at
http://mayhewlabs.com/3dpcb .