I know the 16V head fits the 8V block, so I suppose it'd go the other way.
There'd be other considerations, like dist, compression ratio possibly, different crank gear? Tensioner mount? you also need intake and exh mani, downpipe, intake plumbing, etc.

Layshaft; no balance shaft on the 8v; if head dist, the aux shaft only drives the oil pump. If you plan for block dist, check into whether the gear is on the shaft for it.

Some thoughts, others will know more details.