Hi Jay,
you need to get the front pipe off as the d shaped section will be in the barrel (the finned bit of the engine) whithout work here there is no way you will get any more go or power if you alter the gearing alone you may get a higher top speed down hill or on the flat but you may be pushing the bike up hill. I also pointed out the YEIS tube which can cause performance issues on the V50 (along with worn auto clutches etc). With regard to plastics you could fit some leg shields from the V70A (they had 'mate' written on them) but you must take into account a scooterette was really never pimped. On a performance point of view the following engines will fit V70,V75,V75A,V80,V90 for sure and the U7/U7A may also fit but given the age of the bike if you could get hold of the V80 engine & front exhaust pipe and a FS1 silencer (pre 1977) you will have a bike that will either wheelie in all 3 gears (V50 gearing) or do about 60 in most places (front sprocket 14t, v50 std 11t). tbh with the 80 motor & the gearing set I did manage nearly 70 on the M40 on the way to London from my locale
Regards Jim