I think I have a better answer than a 350 V8 for the 280Z - I have a 1962 215 CI aluminum Olds V8 I've been saving for the Z... It's rated 200hp at 10,500 rpm! They are real screamers - my brother put one in a volkswagen bug, and it became a corvette eater! Kennedy Engineering in Pacoima, CA makes adapters for this engine to fit most any application. I guess I'd have to put fuel injection on it to make it pass smog, though - a little known fact is that the L-jetronic injection found on 280Zs supports 8 injectors - the resistor packs already have 8 resistors, in fact! I think I would go with TBI though, as it's less trouble than L-jetronic and possibly a bit more precise. L-jetronic has too many connectors that always end up corroding.
Just daydreaming, way off the Mercedes subject line!
'77 Jag XJ6L
'77 280Z 2+2
'74 280C "It's a Classic"