Just a stray thought, here, if I may...

Earlier glow engines were lighter, yes, but at the expense of compromising some things: durability, smooth (less vibrating) operation, and overall sturdiness.

More recent engines are sturdier - ruggedly structured to withstand the power protential of the schneurle porting layout. They are better balanced for smoother running largely because the crankweb has been beefed up considerably from earlier practice. That acts as a vibration-damping flywheel.

And, as a by-product of the potentially greater power available with advanced metallurgy and the schneurle porting approach, they are built strong enough to meet those demands.

A more frail engine will flex during operation, and that compromises the metallurgy and machining possible today. The precisely tapered fit cut into most CNC produced engines is irrelevant if the case flexes under running loads.

I don't know the weight difference between ABC, ABN and ABC pieces, but those deal only with the sleeve. The piston is of similar metallurgy for all three, and it is the piston which moves, not the sleeve. A crankcase solid enough to prevent unwanted distortions from running heats and loads IS more substantial than the Fox 35s, K&B 1950's green-heads, and other much earlier engines.

That we have 4-cycle engines of comparable weight and power output is a blessing from careful and effective design, IMHO, not a condemnation of any other engines...

I've seen and flown both approaches. Either way still works, if allowance is made for the intentions of the designers.