But I gotta ask. Does anyone know how hard it would be to swap a 79 280zx 5 soeed tranny into a 71 240 with a 4 speed.

 

Fairly simple. The only differences would be the exact location of the tranny mount & the driveshaft hook ups.

The tranny mount can be massaged to fit, but you might need a custom driveshaft.

 

It's a direct bolt in swap, the only thing may be that the shifter area might need to be cut out in the front (area nearest the radio) slightly for the stick to slide in to 5th properly. I have a '70 with a 5-speed and it works great!

This swap has been done hundreds of times, there's a LOT of information on the web about it if you decide to go forward with this upgrade.

 

You will need the rear trans mount from the '79. The shifter will hit the console a little and Tex is right, you will have to cut about 1/4 from the front of the hole. You can stretch the rubber boot and tek screw it in place. Your drive shaft will fit and it's a good time to replace the front and rear seals and the slave cyclinder.