A horse "length" will vary depending on the physical dimensions of a given horse but is generally assumed to be somewhere between 8 and 9 feet

A furlong is 220 yards (i.e. 660 feet). As such there are probably around 75-80 lengths per furlong and around 600-640 lengths per mile (1 mile = 8 furlongs).

So on that basis if you know the race distance and the winner's finishing time, both of which are fields in the Smartform database, you can

(a) express that time into a seconds-per-furlong or seconds-per-mile basis

(b) convert disance beaten (in lengths) into times by applying the above approximate ranges on a per-furlong or per-mile basis

An example. Consider a 10 furlong flat race run in a time of 2 mins 10 secs (standard times vary from course to course but this would be a fair, unremarkable time for a truly run race). This is 130 seconds in total, which can be expressed as 13 seconds per furlong, or roughly 13 seconds per 75-80 lengths. From this you can see that one second equals roughly six lengths in this instance. So a horse beaten 6 lengths in such a race would be around a second behind the winner.

The standard conversions that you linked to don't seem miles off, but they basically assume that going conditions are the only determinant of the speed at which horses cross the finish line. They are an important factor, but there are pleny of others (race distance, race age band, race class, etc.). The above approach based on race finishing times implicitly takes all of these things into account, and would be equally applicable to Ireland and to the UK.

Good luck.