I imagine you would be fine with the 3.slow As for how long they last...its very hard to tell. Some ppl have good luck with them and some have terrible.
My brother's friend owns an import wrecking yard and has had a 90ish 2wd flatbed with the original 3slow and hasn't had any troubles whatsoever in it's over 300,000 miles
He's not sure how he got around the headgasket problems, actually hadn't heard of them until I told him about it a couple years back.
I'd seriously look into buying that runner, sounds like a pretty decent start.
