Basement Find - need Marx transformer

[grandnational]

Awesome!  Thanks, ADCX Rob!

[ADCX Rob]

Any Lionel, Marx, or American Flyer 40 watts or more transformer will work. Those sets usually came with a 50 watt model:

A 90 watt Lionel 1033 or 1044 would be ideal and give you some operating flexibility & options.

[grandnational]

Hi Everyone - a train noob here, so forgive my basic questions.  My father was interested in mainly HO scale trains.  When cleaning out my Mom's basement, I found his HO trains, but also another box with a much larger scale train (O or S).  After 'Googling' this weekend, I believe I have identified it as a set with a Marx 999 loco (fourth variation: no Marx logo and a solid pilot with rivets but with no horizontal bars).  I'm trying to find out generally what year this may be from (all of the cars are metal, no plastic, there is no box, and all of the swiches are manual turning/no electric) and more importantly, since the only component missing is the transformer, what transformer would be correct for this set (wattage, style, etc.).  I ultimately want to get it running to give to my son.  Thanks in advance for any help you can provide.