Small tractor glow plugs

Working on another odd-ball. Iseki (perhaps should be translated Isuki) TU1900. Need glow plugs. Buddy bought the ones that were supposed to be correct. Nope, too large on the threads. More research indicates that the engine is likely not the original (looks to be an E3AF1 from perhaps a TU320). Ok, no problem. I find a reference for parts. Looks like it might be the correct Iseki part number. Found ONE source on line, new old stock, BUT out of stock. Great. More research.

I have a chart of NGK glow plugs by size and voltage. None are quite right.

So, the question is (I already have an email into a company in Australia that is a dealer and will call some places that I called on Friday without some of the info that I now seem to have), how close does the plug need to be in length? Can it be shorter? How much shorter would you consider to be safe to use? How critical is the voltage. Originals that we pulled out appear to be 9v, the part # I found in an Iseki book is 10.5v. We have 12v on the bus and the entire bus through the glow plugs was open to ground indicating that the last person he loaned this tractor to burned them out.

I love working on dinosaurs that nobody knows anything about. Keeps the brain agile...

It being a Japanese tractor, I would probably check with a Kubota (or any other Japanese brand) dealer mechanic as a starting point. Some of the components on Yanmars, Kubotas, and other Japanese brands are interchangeable. I understand that some of the Bolens are made by Iseki. And as I write this I recall waiting 2mos. last summer for some very common Kubota parts, covid I was told.

have you looked on yesterdays tractors?