Nope...
Won't work..
I would suggest that you contact Julius @ Restorations by Julius 818.882.2825
He sells an electronic tach built by RedLine that goes rite into the 70 RR Ralley dash. And then you can connect directly to the MSD. Also its face has the correct color and fonts..

His website... www.rbyj.com
has more details..

Just my $0.02..