John, that's a very fine looking model and a subject very close to my heart, having worked for BAH from 1976-86. I am just starting my own build of the S-61NM. I also have an unstarted S-61N kit (both Whirlybits).
I must say that Whirybits have done a pretty good job with the conversions, although there are a few things not quite right. Also, the tail numbers supplied with both kits are, shall we say, an "unusual" choice. The S-61N kit comes with G-BEEB which was never on the UK register! The other three are G-BEON, G-BEWL and G-ATFM. Sadly, both ON and WL were involved in fatal crashes. The S-61NM kit comes with G-BCEB (thankfully) but strangely also includes G-BFFJ - which is a S-61N.
Your choice of Abbey Gardens as a diorama is an excellent choice. I was there a couple of weeks ago. On that occasion I flew on G-BFFJ . To be honest, not sure if G-BEON ever landed there, as it was an Aberdeen-based aircraft, and located to Penzance while EB was on major 9000 hr refit, but crashed three weeks later.
I'm really looking forward to seeing the finished model!