Congratulations on your new purchase
It would be nice to see some pictures.
Longines make fantastic watches and in some ways offer the best bang for buck of any Swatch brand.
I am guessing it will be a 7750 although I do think some Longines use the modular DD ETA movement as well. The easiest way to tell is look at the crown. If the crown is in line with the pushers it’s likely a 7750, if the crown is a set lower in the mid case, then it’s the DD module ETA. Either way both are reliable movements that offer good time keeping. Be warned, it’s a slippery slope, one nice watch tends to be come 2 nice watches, then more are added until you need a safe...