Tracking down 24V solenoid issue

After letting '66 FFR 88 sit much too long during brake and seal rebuild (excuse was pandemic, no garage heat, and disc surgery) I wanted to start the landy and test the brakes before I bolted the fenders back on.

I charged up the fairly new batteries (optimas), reconnected the terminals, turned the key, hit the ignition switch and nothing but a loud buzz from the solenoid (original - so 55 yrs old). Double checked batteries - about 12.9 V ea - cleaned all terminals and tried again - still a buzz but no starter engagement. Whacked solenoid with piece of wood. Things engaged briefly, but not a seond time. Still not getting juice to starter, I think. But not sure if solenoid is engaging fully.

So - what's my next step? Should I try to jump the two terminals on the solenoid to see if the starter engages? That would tell me if the solenoid is the culprit. If the solendoid was a cheap part, AND if I saw one that matched the look of the one I have, I'd just swap it out. Neither of those conditions apply. All the ones listed look like square boxes with spade terminals, mine is a round style with nuts holding down the control wires.
Has anyone replaced old style with newer varieties? Who made the originals? They look like AC/Delco 24V units.

Any advice or insights on next steps would be greatly appreciated.

Best

66 FFR registered as OLD TOY
Cape Cod

I've never had to replace one .... i'd get OEM if possible but AC delco ok. you might measure the voltage at the solenoid..... some of my equipment here runs on 12vdc but the starter circuit is 24vdc ......... ??

OLD TOY now fires right up. Whew. A lot of patience, a lot of muttered curses, and a lot of beer.
I'm not sure if it was the whacking on the solenoid, hammering the tail end of the starter, retightening of all the battery clamps, or the sacrificial jigger of scotch whiskey placed on the front bumper at dawn that did the trick.

We shall limp along until the transmission oil leaks get addressed - at which time I may convert everything to a simpler 12V system.

I did come across a good web site on tracking down solenoid issues that might be of use to some future reader. https://startersolenoid.net/starter-solenoid/#c2

Best
Roger B
Cape Cod