SFE
If you are running the standard engine fan is there a shroud fitted?
SFE

Great question. A fan shroud and top tank shroud will make a huge difference

retro666
At the moment a engine fan but that will change later. Is there any issues with the bonnet line on a Mk1.

Not if the Cortina rad is mounted Using its orig holes. .. Tho i may have drilled new mount holes higher to lower the rad in my mk2 escort. It does come close (within an inch gap) .. all good !

SFE
Could also consider a mk2 escort ghia one which I believe has more cooling fins but some loss of capacity due to transmission cooler in bottom tank.
If you are running the standard engine fan is there a shroud fitted?
SFE

All two litre radiators from Ford have the auto lines present.

JVC063, I've owned my 2lt escort from new in 1979 and it didn't!!!
SFE

A 1600 with the mounting bars Reversed is a 2Litre Rad. Also Add the Rad./Fan shroud.!!
 
For high performance, get your Rad. guy to put in a Triple Core when Reversing the mounting bars.!!
 
Cheers

What's the difference between a 1300 and 1600 radiator?

A  1600/2Litre has a larger coolant/cooling capacity due to the extra length from the top to the bottom of the radiator, to the bottom of the Radiator. ... As you wish to run a High Performance 1600 Engine you need a High Performance Cooling System, a Triple Core will give approx. 30% more cooling capacity, the radiator fan shroud is assisting in drawing air through more of the radiators Area.!!
 
High Performance can mean, I want a Full Race Cam, Twin 4 barrel carbs, 12-1 Compression Ratio, you would need to run Race Fuel, or at Least, AV gas, engine build cost may be $10,000, Destroyed by an inadequate Cooling System.!! ... You need to list your build details, then ask the Question Who can Build me a Radiator/Cooling System to Cope.!!
 
Does that make sense,???

OK, if I am reading it right. The 1600 radiator is taller and the 2lt is a 1600 with the mounts reversed. So I need to find a taller radiator with a shroud. The motor will be a step up from GT specs still running the downdraft Webber, a bit of a lumpy cam etc. It needs to be a everyday runner.

For that spec a standard 1600/2000 radiator will be more than enough. Or just triple core the 1300 radiator so you don't have to cut the car up

Send it to a radiator place and just get it flushed and unblock the core tubes they block up over time once clean it will be like new again