Yep, have to agree with Nos on this one.
http://www.old-omc.de/index2.html
has scans of various sales brochures - even in 1977, the 70Hp was manual tilt, and PTT was an option on the 140! (hernias supplied free of charge!
) At that time, PTT was a massive luxury.....
If it's in such good nick, it's probably worth keeping it that way. The chances of finding something to fit are slim, and even if you do, no matter how shiny & good nick it looks I will guarantee you'll spend the entire winter drilling out & helicoiling sheared bolts. (having done various repairs on a '71 vintage Johnsorude 25Hp) If it's a classic boat you have, I'd be tempted to leave it well alone if it works!
I've been trying to do the same with mine (1978 vintage), and without fail any PTT unit that has come up has been priced not much less than I paid for the entire boat, as they are like the proverbial rocking horse droppings...... I think (but need to measure one to confirm) that the clamp bracket may have carried forward to the "new" 3 cyl autolube 50 / 60 that replaced mine around 1981, but until I find one to measure..... I'd still probabyl be cheaper with a new machine.