I would agree about getting it here, it is good to support our host.
That being said by saying it doesn't need to be authentic makes me think you want something reasonibly priced.
That said the bulb on a "universal" guage will go in the top neck just like the factory unit. This also gives you the oportunity to relocate the guage. I have a couple of 45's I have done this to. One just the oil guage the other oil and temp. One quick note, when relocating the oil guage remember this is a low pressure engine, a guage from a earlier D 15 or 17 will work though.