Everyone is interested in "newer/lighter " engines - There may be a bit of "wistfulness" afoot ----
From what I have seen in single cyl designs -- 2.5 lbs would seem to be a pretty light target - small plug - thin wall cyl, slipper piston etc..
The extra bits tho - still weigh the same - a decent, quiet exhaust setup - close to 10 ounces -a blatty stack, - a lot less.- an ignition -2 ozs min - we had some of these done once - using a coil mounted to the engine - fed by a small electronics package - the batt- another 2-4 ozs
The prop? well these vary by a 3-1weight factor! -spinner etc..
Bottom line - the % difference in the entire"powerunit" will be quite small.
Getting a very light , very smooth power package is still quite a trick.
The big rub is that the torque reaction really is tough to control.
Overbalanced cranks and trick ignitions really help here but a poorly adjusted carb and a light , flexible prop , can ruin the best efforts for smooth operation--regardless of the mfgr.