What intercooler is it? Ask him if it a complete kit? Piping, intake elbow(this is a key part),connectors, instructions? Front mount intercooler? Is it a kit that is made for the 84/85 TR's? If it is a kit it should be pretty straight forward install. You would have to mount the intercooler, run the piping, and re-clock the turbo.
When I bought my '85 GN it was pretty much stock with a spearco intercooler, bigger fuel pump, adj. wastegate, and adj. fuel pressure regulator, that was it. That ran a 14.05 in the quarter mile with stock size 215 tires on it. Easly capable of 13's.
How fast do you want to go? For 12's you will most likely have to at least upgrade to a 87 turbo or aftermarket turbo/injectors. But, intercooler and basic mods are an easy 13 second pass with a 84/85 TR. Stock 84/85 is a high 14 to mid 15. So, its that easiest bolt on power add for the 84/85's, I think.
Nick.