The spec in the workshop manual for both TR3 and TR4 is 60 degrees, plus or minus 3 degrees. I've no idea what drugs the Rimmer Brothers are taking, but 32-38 is more appropriate for an 8 cylinder (Stag with dual point distributor is given as 34-38 in the Stag workshop manual).
Gap and dwell are directly related, you change the dwell by changing the point gap. The relationship is set by the shape of the point cam. Either method of measuring should be good enough; but at least in theory the dwell is the more important measurement.
My problem with setting point gap is always that it changes as the locking screw is tightened. If I get the gap perfect with the screw loosened just a bit, so I can barely move the point arm, it will still move during the final tightening. Measuring dwell instead of gap doesn't help with this problem. But usually, by using two screwdrivers at the same time (one to hold the point arm, the other to tighten the screw), I can get it pretty close after 2 or 3 tries.
Unless you are running really high rpm, dwell angle isn't all that critical for a 4 cylinder anyway. It's more so for 6 cylinder and even more than that for 8 (because as you add cylinders running from the same coil, the available dwell time per cylinder goes down).