It's probably not worth the trouble, but i've been having these ideas for a historic race motor, which means there basically is no capacity increase aloud from stock, so in my case 1300.

The specs I had in my head at the moment were

Counterweight 69mm crank
not sure on cam but with 1.4 ratio rockers
dual port 1300 heads (if aloud not sure.. preferred though) 40in, 35out
dual kadrons
mallory dizz with vaccum advance, if it wasn't for a racing class i'd have an ignition box as well
stock style muffler with internal baffles removed
and anti-surge sump

as said if it wasn't for a historic class i'd leave the stock cam, add 1.4 ratio rockers, have the ignition box and have the dual port heads with stock valves, with the kads, I think maybe it would be a pretty efficent motor, then again I could be talking crap like usual... (thinking about it if it was for a class you'd just increase the capacity!!)

my insipration for this motor is the old austrian rally bugs
http://www.1302super.com/page35.html 
http://www.rallybugs.com/ 

love to know your thoughts

Hp (DIN): 110-120 at 6000 rpm (rpm limit: 6700)
Torque: 13,6 mkg at 5000 rpm

those are some great figures for a modded 1600DP

dunno about how the 1300cc would go, but im sure if it had those specs it would go alright!!

tbh i was thinking the exact same thing with my car the other day. what would it take to make it a fast and strong 1500.

but its only a SP so i dont think its worth doing anything to. but i mean if u own a DP then go for gold man! 110HP @6000rpm cant be bad!!