The MKIII is rated at max 5 amps for coil switching. Not sure what the current being drawn through the coil 0008 is - if it's a 3 ohm primary winding, then you're basically on the limit, and the MKIII unit will run hot. You could always install a ballast resistor (1ohm, 25W) in series with the coil primary to bring the current (and this heat) down, and shouldn't really affect the spark. It may even reduce the pitting wear on sprak plug electrodes due to over-voltage.
The Micro Digital systems require suppression caps, but also provide a greater range of advance (15deg) at lower revs( 2500) compared to the MKIII (10deg at 5000).
Does the 77 Bonnie have 2 coils, or one 3 ohm coils - your post is a bit confusing on this.
Did the Micro Digital system fail on it's own, or was it an ID Ten T error?
IMHO, I'd go with buying another MKIII, and a ballast resistor. That way, you can swap between bikes if one fails, without any changes except the physical box move (eg no need to re-time), and the ballast resistor will keep the 76 box cooler.
Per Ardua Ad Astra
(Through difficulties to the stars)