That looks hard core! I was figuring that as its an old frame with horizontal ish ( def not vertical dropouts) I should be OK and add a tensioner if I really needed.. I'll look into shorter cranks I think and also the pedal profile. What sort of gearing would be advised for the rolling countryside of Northamptonshire?
We’ve ridden fixed gear bikes 100 to 200 km on rolling country with a few steeper long hills. I’m from the Upper Peninsula of Michigan, USA. In 2014 I rode Hadrians Wall Cycle Way, which, in the middle section, is similar to here. For this type of riding 44x16 would work, but that might be too easy for you, depending on you conditioning and age. Remember, you have to pedal downhill as well, you never rest your legs. I guess it depends on how far you want to ride. These bikes seem to have a speed where they are happy at a particular gearing and they like to go fast if you have a light weight frame. Of course, a good front brake is a must as are toe clips. A good brake saves knees. Toe clips come in handy for emergency stops. You can do a hockey stop with toe clips with a little practice. Emergency only, you don’t want to bend a rim. You can also fold a front chainring trying to do an emergency stop so a strong crank and chainring should be used. You can fold a robust chainring trying all your might to stop a fixed gear. My son folded a heavy duty chainring and jumped off the bike to avoid being plowed down by a cab in NYC. The bike did cartwheels and landed in the middle of an intersection. Some old track bikes had three arm cottered cranks and that won’t stay straight for us as it was only intended for acceleration and not forced resistance. Again, these things are fast. Wind can really be detrimental to you on a longer ride as you can’t compromise by dropping to a lower gear. The wind is something you should think about before a long ride. Your pedaling technique will improve riding fixed and if you mountain bike you will just naturally be able to pedal a lot more than someone who doesn’t ride fixed gear. You can pedal almost all the time, over obstacles and avoid more pedal strikes on the trail. I hope others chime in as I’m no expert, I just do it with what I have in my junk stash, but 44 x16 seems ok to me. A tensioner is necessary, you have a lot of forces.