Hi Marko! Welcome!
Nice car you have there! A lot can happen in 34 years. Do you know if it's still the original block? Do you have the fender tag? From the VIN # if the 5th digit is an "H", you're looking at a 340. If the VIN has a "G" as the 5th digit, then it's a 318. "74s had a 360 in place of the 340. Best to crawl under the car and check the casting numbers on the block.
Just by looking as you car sits in the pics, I would guess that it has a 340 as it has the rear valence cutouts, chrome exhaust tips, performance hood. I don't think the 318s came with those. The 340 could be had with out the Rallye option I believe. I would think that your car is not a Challenger Rallye since it doesn't have the front fender louvers, but again, a lot could happen in 34 years. Again, this is how your car sits. If it has a "A57" code on the fender tag, then it has the Rallye option. All '73 and '74 cars had "JH" as the first digits. '70-'72 cars had "JS" for the R/T and Rallye cars.
Sorry if I missed but do you have the Rallye gauges? 4 round gauge pods of the same diameter?
Feel free to ask any questions! Lots of people here with lots of info!