Most of the ebay injectors are trash, many members have opened them up to find rust and dirt inside, even though they appear clean and rebuilt on the exterior. You won't hurt anything leaving the pump in for now but I wouldn't leave it in forever.
Like you said it looks like that purchase is closer than you may have initially expected but if you think about it, you will have a bullet proof brand new injection system that will last you another 150k and up. If this was a psd you would be looking at twice the cost or more.