Dennis & Bill, No reason not to use the RX-8 coils, the EC2 will work with them (be sure to specify this when ordering EC2). The RX-8 injectors are fine too, very compact and light. The EC2 now has the ability to be setup for the different primary & secondary flow rate injectors as used on the Renesis. It is a pain to adapt the Renesis block to fit the earlier 13B injectors anyway.
The regulator is not what you have on the engine. That is a pulse damper. Regulator is in the fuel tank I believe. You will need a separate 3 port (manifold referenced) regulator.
The RD-1C requires that the engine be equipped with the auto counterweight (rx-8 model) and a 1986 - 1991 RX-7 auto flexplate (it fits). Don't use the spacer on RX-8 auto flywheel if you happen to have it.
No problem removing one tension bolt at a time, won't hurt anything.
Tracy