Vintage Cars: 450SL sluggish acceleration, vacuum leaks, fuel stabilizer

Question
I have a '77 450SL with only 80 000km on the odo. Great shape and FSH. It's been standing recently for a period of 5 months and just took a trip of 1 000 miles (1 600km) noticing some sluggishness at pull away till about 100km/h. Just replaced new plug wires completely and new spark plugs. Had a service done in March 09 and was running well then.

Answer
sitting causes petrol to break down, and  clog injectors  I would run some injector cleaner and run it hard. I always put in fuel stabilizer if I know I will not be driving for 30 days or so.
You may want to check fuel filter as well . Also check for obvious vacuum rubber line  breakdown, or vacuum leaks.