Good Day to You,
I would ask you to be patient if I go through something you have tried. Your question was posted under radiators so am not sure of model of farmall tractor or if a farmall. If you need to know more like firing order, tolerances for compression will need more specifics on tractor. I am going to go through this systematically. It takes 3 basic functions to make an engine run, Spark, Fuel, Compression. Will hit each one of these to make sure we covered all bases even though you have changed a few of these things.

1. Spark, make sure that ALL cylinders are firing, the spark should be bright. A Timing light can be used or an in-line spark tester. Or remove plug and test by grounding it out watching for the spark. If you have good spark in all cylinders then move on to Fuel. You mentioned changing the coil what of the distributor. The timing may be off as well check the timing.
2. Fuel, Is there fuel present in the cylinders, Fuel pump working, clogged fuel filter start working backwards if fuel not present.
3. Compression, Check the compression in all cylinders and compare them with one another. Low compression in one cylinder would mean possible bad rings or faulty valves. Low compression in two cylinders that are adjoining and they equal to each other would be a head gasket as probable cause not always to you have leaking radiator fluid with a bad head gasket.

HELLO,please what is not starting,i will really appreciate if you can re-type the question.
name and model number.

take care