I was looking a an old ECG book and the difference ecg shows is the 145718/ECG533 has a 1.5meg internal focus resistor and the one I have 145719/ECG537 has a internal 4.7meg resistor. You may not get it to focus with the 145719.
Both of the above are a 5 step tripler.
The 146356 is a 6step.
I don't think you will get either one to work correctly in your unit.
But if you want to buy them $20 each both are new ,never solder on in RCA boxes.
If you need any other parts contact me I closed my shop in 2000 after 25 years along with parts /schematics from my own and from buy outs of other shops plus from my dads shop 1950- up.
Also might keep in mind on the following web site has old RCA parts
http://www.fouraker.com/. Excell distributing in Cincinnati
has old parts.
Its possible I may have other triplers in unsorted boxes, will look when I get a chance.
Doug