I guess "how old" is the first question! ("Old" to someone like me is probably a different definition to some of the other forum members!). Have a crawl (use the advanced search funtion) to see if there's many (or any) posts about it. Also the older engines are arguably easier to service - if you know what you are doing.
...and if it's a 4 cylinder expect it to drink like a 60!
s for PT it wasnlt until relatively recently when "small" engines like that were PT. - even in the early 80s PT was still an opition on things like 70 & 90 HP. It will either be one of 4 things:
a) non PT with the "lift assist" rams on the outise of the clamp.
b) PT with powered rams, on the oputsode - there will be a hydraulic pump unit lurking somewhere inside the boat.
c) Non PT with the lift assist ram inside the clamp brackets.
d) PT version of c, possibly with two extra rams poking upwards at 45 degrees when the engine is up.
If you have c) , D is relatively easy to retro fit,
if you have a), turning it into B is mostly made difficult by the lack of donor parts (although I believe the Merc sterndrives might have suitable components?)
thing with b) is you end up with a mess of hydraulic pipes.
As you say, trading the engine in later might be a better option, but if you enjoy a wee engineering challenge, most engines can be PT upgraded.
A small leak shouldn' be a problem (you can get repair kits for £30 odd - but be wary if it;s at a seam as that will be a LOT more difficult to seal. - take a jar of heavily soaped water (washing up liquid) & a paintbriush with you to check.
As for the painted toobs - have a search - this has been covered before (and I can't remmebret the conclusion!)