I've been thinking for a while to get up to Scotland to get the 92's and 73's for Haulage, can anyone advise whats the cheapest way of doing it and minimum number of nights required to get them all in.
It doesn't really work like that. There are ten 92s that could theoretically work the sleeper - 92006/10/14/18/20/23/28/33/38/43 - and six 73s - 73966-971.
Clearly the cheapest way to get any of the engines in for haulage is to book seated accommodation in the low season, for example on a weekday in the winter.
Other ways of getting 73s are to book a journey on the Fort William sleeper wholly within Scotland as it allows 'day' passengers. The 73s may however, not be hauling if a 66 is on front, instead only providing 'hotel power'. The Aberdeen portion gives the chance to get 73s on their own for haulage. The summer months have typically seen less 66 involvement.
It could take a while to get all the engines for haulage as some of the 92s end up on restricted duties, and from time to time more substantial maintenance is underway. 92032 and 92044 aren't equipped to work the sleeper since the Mk5s started.
If you can afford the time, travelling at short notice based on what can be seen working on RTT is the way to pick up the ones which done come easy.
Finally, for 66s, you basically need to keep an eye on swaps between Doncaster, Millerhill and Craigentinny on RTT, and even then you can get caught out.