Maybe Hans Moust will weigh in here, but I have owned three 1960s Guild Marks over the years and have two now.
The line was designed by Carlo Greco and production was overseen by him. The Mark I had an all-mahogany body and was built a bit sturdier than the higher-end models since it was sold as a student guitar. But don't let that scare you away. They are serious guitars that sound great, and, being all-mahogany, have a unique sound.
The higher-end Mark VI and VII models are very sought-after and command high prices. Lightly built, they are on par with the best classical guitars made anywhere.
In between are the Mark II - V models. My Mark IV has pearwood back & sides, which gives it a bright sound similar to maple, but it's very lightly built. Other midline Mark models feature mahogany, Indian or Brazilian rosewood, and, if they're in decent shape, the midline Marks are almost always bargains when you find them. They made most of them in the 1960s in Hoboken, NJ and, after 1966, Westerly, RI. Production ended in the 1970s, I believe.
My Mark IV as found. It's in the shop where the split bridge will be replaced and the ugly tap plate will be removed. I got the one recently to replace a '67 I stupidly sold several years ago. The Mark I is a delight to play, with dark mahogany fullness of tone.
My Mark I