Just thought I'd post this information for those OMC owners who may come across or have the first generation of OMC's Prestolite division power tilt mechanism. It is tilt ONLY, no trim.
This early system works off a single "power piston" which replaces one of the two lift pistons on the earlier transom brackets. The parts diagram below states 1968, but this system must have been around earlier than that as my 1960 Evinrude V4 has the three bolt hole mount for the motor/pump assembly on my starboard side bracket.
Early drawing complete with switch plate for the helm. The flex hose has a small piston on the end that presses on and unlocks the engine's tilt release.
It means that the system is only for tilting the motor to a full upright or full down (into the water) position. The system isn't strong enough to hold a trim position in between when the engine is under power. The tilt and trim setups usually had two hydraulic pistons.
Here's a tilt/trim. Two pistons. You can trim with a tilt at low speeds but if you "hit it" the lower unit will go down under power.
There are units on ebay but they are getting scarce and get premium price, even ones that need a rebuild.
Cheaper to buy an old junk boat with an omc hanging on the back with t/t. That way you get a trailer, hardware, bling, controls, the t/t unit and $100 worth of scrap alum for the motor.
Been doing that for 30 years