...the distancing on 6 cog freewheels is pretty similar on most makers' freewheels, so 6 speed Shimano indexing is pretty forgiving with regard to freewheel brand you use. That said, Shimano freewheels are so ubiquitous in the used parts stream that I usually use one of theirs in a freewheel setup.

You sound like maybe you are going for freehub. The six speed freehubs are all pre-hyperglide, AFAIK. You didn't really elaborate on the rear wheel you now have, if that's what you will be using.