I just purchased a 74 Vette.  It has a 350 and is an automatic. 

You can change your car from an automatic to a manual tranny but it's not as simple as some would think. Consider the price of a flywheel, pressure plate, clutch disc, pilot bearing, clutch pedal with brackets and linkage, shifter, new console and boots, in addition to the cost of the tranny.

My mechanical ability being zero, I checked into the cost of this conversion on my 62 and discovered that I would be ahead of the game to sell my car and find one with a 4 speed. This was back in 1993 before the prices on the C1 and C2 skyrocketed. I was lucky and found what I was looking for at Knoxville for less than I sold my car for.

Good Luck on whatever you decide, and enjoy rebuilding the car with your 2 sons. 

From what I've heard, the transition is possible, but one of the most difficult parts can be getting the clutch peddal in place and correctly mounted.

All of the parts are available, either new or used. The pedal assembly will be a BIG pain to swap, unless you plan on gutting the dash anyway. Also, the frame will not have the bracket for the Z bar linkage, but it is available, and can be welded on.
The removable crossmember is a big help, as four speed cars were welded.
Along with everything Jim mentioned, you'll need a different speedo cable, as the 4spd come out on the pass side of the trans, instead of the driver side of the auto.
Originally, the '74s had a Borg Warner trans, but a Muncie will also fit and work.
Of course, if money is no object , you could always go for a 5 or 6 speed conversion...

I personally think it is not worth the effort to convert from an auto to a standard, but that's just me...I'm too lazy anymore for that kind of commitment!

I once considered doing the conversion on my 75. I could do the work myself but after looking at the totality of the job it just didn't make sense economically. I agree with Jim. It makes more sense to find a factory 4-Speed car. I love my 75 but it's just not as enjoyable as it would be with  a manual tranny. Maybe soon I will have one of each. One can only hope!

Scott

Instead of the conversion, you might want to put an overdrive automatic instead.  The mileage will go up, and with a shift kit you can manually shift to your hearts content.

I put a T56 6-speed in mine and it changed  the whole charactor of the car. Installing pedals wasn't that hard after removing the steering column. I used the hydraulic clutch from a 95 chevy Z28. The shifter will need some fabrication to correct its geometry and the crossmember needs modified and the driveshaft will need shortened.

David: