EFI boot after OS X El Capitan install part 1

Attempting to install El Capitan to cloned 10.6.8 western Digital usb external drive.

Model Name: iMac

Model Identifier: iMac7,1

Processor Name: Intel Core 2 Duo

Processor Speed: 2.4 GHz

Number Of Processors: 1

Total Number Of Cores: 2

L2 Cache: 4 MB

Memory: 4 GB

Bus Speed: 800 MHz

Boot ROM Version: IM71.007A.B03

SMC Version (system): 1.20f4

so its a Mid-year 2007 iMac, which is on the approved list for El Capitan

I've booted to the usb external drive

Downloaded El Capitan

run the install [looked at its log, its bless'd it]

however after it says its going to boot to this drive, it doesn't find it and boots to a different usb volume

StartUp still shows the old volume, and it will boot to this, as 10.6.8 [and the El Capitan install is still there]

however, under "option-key" start up, it shows this volume as being named "EFI boot"

and won't finish the install.

next step?