Hi Dave: Welcomed to the forums, I see I didn't post quick enough as Willie and Chet both mentioned some of what I did! I'm David in Coarsegold, Central Calif., which is in the foothills North of the North end Fresno by 31 miles. I've been involved with HO scale model railroading most of my almost 72 years in Dec. I also had a 5' x 9' layout around the time you did too. During that time I met a fellow whom I knew as Mark Raymond, who was an Engineer for the SP in Fresno and he taught me to build my own switches using code 70 Railcraft weathed rail. They are now named, Micro Engineering, great track btw.
Yes, things have really changed but a number of older RR's, like myself have decided to stay in 'DC' as we are single operators and don't see the need of operating two or more loco's at the same time unless in a consist such as double headed or as a helper if the need arises? And various guys have said that the sound can get tiring too after a while, I guess it would depend on how high you had the volume set. Anyway while the chuff and some other sounds are nice I can use my Cell Phone and an App called Railroad Compaion an in expensive down load that allows me to play the various sounds as well as get the chuff, ring the bell and blow the whistle to send signal as I wish, so with that, it's like having both worlds in 'DC' without the added expense. Blow the various whistle signal alone adds a lot of realism to operation. Not that it's always necessary to do that but available when you want to do that.
So possibly your old transformer and equipment will work just fine if you stay in 'DC'. The thing you may want to do depending on the type of wheel sets on your cars, might be to change them out, if you already haven't to the newer RP25 contour which is self centering as the cars roll down the track. Metal wheels are preferable and do offer some natural rolling, clickty clack if things are quiet enough.
I've been work on my current layout for a long time, due to various things that have taken place in my life, as well as that hand laying all my rail and making my own switches is time consuming but I love it as I can design a switch to meet the needs of a given situation depending on if I can maintain the 20* radius I established when I started building my current 10' x 21' layout which is a folded dog bone with a lower line of about 45"s in height and a upper line of about 54"s in height for enjoyable viewing for me at 5' 9" tall as well as others that are about my same height. This is an around the wall, free standing L-gerder type of frame work that was meant to be 30" deep but has turned out to grow deeper at various locations. I have pictures of my bench work on the site here under my site name. It is light weight yet very strong especially once 45* angle bracing is added.
I hope this helps a bit Dave
Ps: I guess now we are going to have to distinguish between you and I by David in Coarsegold and you at your location?
Be sure to stop in at the, 'ANPL/Jefferies Dinner' down the main listing for coffee & do-nuts plus conversation of your choice except Poly-e-tics or Re-lg-ion.