Submereged Surf Vs Recondition

[MarzTraveller]

Looking for some advice here. . .
I have an 89 surf and it is getting "tired". I thought, while it still actually goes, instead of shoving a replacement motor into it [from Japan or where ever], that I do have time at the moment while its on its last legs to recondition another motor and put that in while I am still mobile - that way I know where I am at exactly with life expectancy!
So I am looking around for another suitable motor or whole vehicle to recondition because...

♥ I LOVE MY SURF!

I have a couple of choices to look at, but one vehicle has been submerged in fresh water some time ago and the water is still in there "just below the lifters", which does not sound at all good.

I haven't seen the truck yet and imagine it is all rusted up inside the engine. o_O

*QUESTIONS *

>How long can a motor have fresh water in it before it is "too late" to be salvageable?
>Is it even worth looking at a submerged vehicle to recondition?
>Can any year of Surf/Hilux be suitable to replace into my old truck or do I stick with certain years?

Thanks

Marz