The engine I recommend Is the V12-2 if you dont have the DLC Using these figures
Position
X: 0 Y: 0.3550 Z: -1.0300
Rotation
X: 0 Y: 0 Z: 0
Scale
1.0200

although I have not found a good way of connecting the muffler, and it is a little lower then the engine cover so it can look a little weird at times, if anyone has any tips or or a better placement of the engine that would be great, this is assuming you have no DLC and only using base game stuff, I tried to make so it didnt collide with anything, but the transmission still goes slightly through the back, but you cant see it outside of the car because of where the muffler is
Also if you dont know how to change the engine, when you click play it should open a smaller page that asks what you want to load, the second option is the editor, and it is a lot easier to figure out then you would think, but if when you click play and no smaller page opens then you clicked the "use always option" at some point when you opened the game, I dont know how to turn that off since I dont use that option on any game, but a quick search in the base steam discussions should help you.