Okay, here's the lowdown on portland cement in refractory mixes. Or any portland-based cement product, quickset included. Will they work? Yes. Will it occasionally work for brass/bronze temps? yes. Will it last? Probably not. I must confess, i built my first furnace from portland, sand, and vermiculite. I used it for almost three years before it deteriorated to the point that it was pretty well worthless. It had been repeatedly patched, and chunks fell out every time I went to use it. Portland undergoes a chemical change at high temp and loses strength. At a high enough temp(brass/bronze, or very close to it) it turns into a flux and the liner turns to a gooey glassy mess. Ask me how I know.
It will work for a first furnace. The perlite (or vermiculite) acts as insulation in the mix, unfortunately they are also a flux at high temps and aid the portland in its catastrophic downfall.
If you can, and can afford it, get commercial refractory. Get the highest temperature rated stuff you can, this way if you do attempt iron in the future your furnace will hold up. Try to get at least 2600F, 3000F+ would be better. Don't bother with the insulating castable, get dense castable and add ground up foam to the mix to get the same insulating qualities. if you can really swing it, and where you are using propane you want the best insulation you can get, go for Kaowool with a thin hotface to prevent mechanical damage. It will also heat up the fastest, and your time to the first melt will be reduced.
if you can't find a refractory supplier (check with mason's suppliers) check with pottery places and get some clay. Fire clay is fairly common, Kaolin (EPK is one type) is a purer clay with a higher temp rating. Use the shredded foam trick with this too. The only problem with clay is that it tends to shrink some on drying, this can be counteracted by adding sand, grog, and alumina (the pottery place will/should have that as well). It can also take a while to fire it initially, but if you do it right, you will have a furnace that will last indefinately.
Hopefully I didn't confuse you worse, but honestly, I would skip the portland-based stuff and try to find something else. it will ease future frustration and you will be more pleased with the results. It's like asking if you can tear down an engine with tools from the dollar store. Yeah, it can be done, but the right tools make it a lot easier.
