I fabricate small brass components (by silver soldering) and the only problem I really have is where some parts are much larger than others. It is very easy (I've found) to melt the smaller parts if you don't take care. I imagine your pump will be quite large – so will need a fair bit of heat.
These days I try build up the heat around the components a bit more gradually, allowing everything as far as possible to warm up evenly and I often use a specially designed brazing hearth to help with this. This magnificent sounding bit of kit is actually a large coffee tin with a hole in the side which is lined with Kaolin Wool! You sound like you might need something a bit larger but the idea will be the same. I purchased the Kaolin blanket here (see link) and it works very well and has lasted a surprisingly long time.
**LINK**
I also try to make my smaller component parts so they either slot together and/or are pinned/screwed where possible. I know many modellers use iron wire to bind things together but I find it easier to make the components hold themselves in place and where necessary machine away any tabs/pinning afterwards. It is obviously easier to plan this before you make the parts than when you come to braze them (again I learned this the hard way). Your larger pieces may not be such a problem.
My apologies if there is any element of 'egg sucking' & 'teaching Grandmothers' for you here George.
IanT