1980's roadie converted to fixed gear with 700c wheels (originally 27") - it can be done
bassflicker wrote: where do I make the measurements to know exactly how big my frame is?
There is no straight answer to this as different countries, different companies and different people all use different methods and a 62cm frame from one company might be quite a bit larger than from another company.
A typical method and one that causes least confusion provided you tell the person what you're doing, is to measure the length of the seat tube, from 'centre to centre' ie, from the centre of your bottom bracket to the intersection of the top tube and the seat tube. But that's only part of the game, the most important measurement is the length of the top bar, and again, centre to centre (intersection of the tubes) is the best way - this is the most important measurement as it describes how far you'll have to reach to get to the handlebars.
Rather foolishly, I raced out and ordered a set of deep V's with a flip flop, the size being 700. I've realised this will probably screw me trying to fit a brake to the bike.
Nothing foolish about that at all - they're an excellent wheel (which is why they're so popular) and it's the standard sized wheel now so you've got your choice of tyres (27" tyres are hard to get).
You will need brakes with a very long reach. Tektro make excellent brakes with a range of reaches - the Europa above is wearing their R365 which have an enormous reach (my brake pads are in the centre of the range) and they work very well. I paid $65 for a pair of calipers from my local fixie shop. The old brakes that came with your bike should work too - it's miraculous what new pads do to a set of brakes, I've only just fitted the Tektros after three years as a fixie.
Can i solve this by fitting a new front fork?
No need to at all - just buy the Tektros, it what everyone else does.
I'll be asking for info on gear ratios for the crank and chain lengths etc.
70 gear inches is a good, urban size - not too high, not too low and produces a cadence of 90 at around 30km/hr. However, I suggest you start with something lower until you learn the tricks and methods, simply because the pedal forces are lower.
It depends on your chainring of course, most people (the above bike included), just start with the inner ring on their road crankset - simply remove the other ring and fit shorter chainring bolts (from the lbs). This ring usually has a tooth count of 40 on them older bikes, so mate that with a 16 tooth rear (ie, 40x16) and you get your 70 gear inches, but I'd start with an 18 for a lower gear. If you've bought a new track crank set, you'll probably find it's got a tooth count of 48 so you'll need an 18 on the back for your 70 gear inches (ie, 48x18) - that's what my Europa is running.
Chain length? In excess of 100 links probably, but it depends on your gearing and the length of your rear fork - most bmx chains are too short but I've never had a problem changing chains - just buy the longest one in the shop the first time, and cheap works well for a first try.
On the wheel measurements - imperial sizing (the 27") is to the outside of the rim - french (700c) are to the outside of the tyre ... from memory, hence your confusion with the ruler.
As said by others, it's all on Sheldon's website, and he has a section devoted to converting your old roadie into a new fixie.
Have fun. It's a great way to ride.