Kel,
Getting the lathe level head to tailstock is desireable, but not super critical.
Getting the lathe level crossways, the same all along the bed is crucial to having an accurate machine. That is what I was on about when I mentioned getting the twist out of the bed. Even large industrial machines can have a twist on their bed, so mass really doesn't come into it.
The easy way to imagine the problem would be to put a centre in your spindle, and one in your tailstock, and see if they touch on their tips perfectly. Difficult to do as the tailstock is at the opposite end, but it would show the problem.
An engineers level would always be preferred, but if you only have a small home bubble level, anything is better than nothing, as long as you don't go turning it around when going along the bed, and try to mark it so that it sits in the same position across the bed in relation to the ways, it should give you a reasonable starting point, then when you do get to beg, borrow or steal a proper engineers level, to get it exact, you will find it very close.
I do recommend people buy a proper engineers level, I got a couple of mine second hand off eBay for a fraction of the cost of a new one, and they can be used for other things, not just for bed levelling.
John