Hello Corduroy,
From other mowers that I have seen like yours.
The colour you have is the original.
Early 80's had a light hammered green with a orange B&S
60's to 70's a dark hammered green with orange kirby's
Original engine on yours is a black briggs and stratton 3.5hp. I have one available thats currently on a Victa imperial. (I'm in Perth) so yes, can sell to you if you want original but prefer to sell complete with Victa. You can then put the tecumseh on the Victa then sell that.... win, win.
Let me know.
Your mower age is late 80's to early 90's.