this brought to you by the same fred who always helps and wants to share knowledge with his engine loving community. this in contrast to some people who constantly pick fault with others work and make unbackable statements... not naming names.
ok, so clamp it by the flat where the injectors go in, and the round back, level it off the bumps of the injector bosses, and machine the side that is up to be flat.
then roll it over and do the to middle bumps to give you something to hold the other side by :
and then the back opposite where the injectors go in :
and then use a straight fluted tapered roll pin reamer cut to the right length to give you the exact diameter you need to ream them out to the correct size. a near mirror finish is critical for proper sealing of the Orings under fuel pressure.
i used a 10mm metric reamer (metric has a 1:50 taper and is measured at the small end.) i had to take about 25mm off of it to get the 10.7 i wanted.
i had some special ally cutting fluid, but left it at home... tried std stuff, very bad. better dry. check your cutter to ensure concentricity before trying it. mounting it in a chuck was not good enough in our case. we had to use a collet for it.
you can now use the machined flats to level and support the rail while boring it out.
the std lead in taper is sufficient. i tried to put a bigger one in on a spare, and ruined it completely... (just practicing)
the short lead in is preferable anyway as the rx7 injectors are about 2mm shorter than the stockers.
you want a very slow cutter speed for the reaming or the bit is likely to chatter when the load comes off on the way out. this will also ruin your bore.
i hope this helps someone in future.
enjoy :-)
fred.