I had the same idea a couple of years ago,I have the same engine and tow a
heavy speedboat in the summer with my 90.
The 19j engine is a notorious high revving and heavy breathing engine and
prone to all sorts of engine failure.
It can just about cope with the extra power from the turbo.The fitting of an
intercooler plus tweaking the fuel pump would be too much strain on this
engine.
This was advised to me from  someone at Allisport who is a regular on here.

I assume we're talking about the old turbo-diesel engine, and if so, while
adding an interecooler (or a bigger one) is an excellent plan I'd be wary of
trying to up the power or boost too much on that engine.

By intercooling, you lower the charge temperature, which is good.  Having
done that, you get the chance to up the boost a bit, and up the fuelling
accordingly, and get more power.  The main problems you get with doing that
without the intercooler are down to overheating and the risk of melting or
burning pistons and so forth.  

Basically, with that engine, and at a high mileage, I'd take it a bit at a
time and keep a keen eye on the operating temperature.

Same applies to any engine, in fact - if you increase the power over the
manufacturer's settings, you risk losing reliability/longevity.

Remember you have to put in more fuel as well as more air, so the fuel pump
needs adjusting.
Probably better to leave well alone in view of 'Bones' comments.