"The van I am looking at has a 1991 2.8L non-turbo. I have seen that some say this is not a great engine? Head issues and not great MPG? Others had told me previously that they thought these were good, so I am confused."
When I started researching Hiaces nearly 2 years ago, 2.8L non-turbo had shining reviews from around the world with frequent references to the 'bullet-proof' engine. I have owned a 1991 2.8L 4wd Hiace (Automatic) here in the Okanagan (BC, Canada) for nearly 1 year (~25-30,000KM?) and have made several trips over the Coquihalla Hwy to Vancouver area & back. Yes, it is a little sluggish at times, particularly if you don't take the hills right, but for cryin' out load, lets face it - if we are looking at Hiaces, we are family folk in the mini-van market, so 'cool' and 'fast' are all relative terms.

. The space and general functionality are hard to beat, and if I ever stop to wonder what I might replace it with from the local market, there just isn't anything in my opinion that even remotely compares. My brother-in-law owns a 2006 Sienna (2wd) - very nice van, and certainly has the classy new look and smell, but even if I had the $ I wouldn't. There are just too many great features of our trusty old hiace to justify trading it in. And in fact, with the right sized tires, a set of roof racks and a canoe on top, it actually does look pretty cool... for a family van.
Of all the fuel additives I have tried, so far Lucas fuel treatement seems to provide best performance - no smoke and noticable improvement in acceleration. 100 km/hr comfrotable hwy speed - how much faster do you need to go? I tried it up to 130-140
once in the early days just to see what I had bought; seemed fine, but probably not healthy long term and no-one should make a habit out of that anyway due to safety & local laws. Best mileage since I have owned it was 26MPG, avg 24MPG, but without fail letting the fuel level drop below 1/4 tank inevitably results in poorer acceleration, mileage, and smoking exhaust. Not sure if I could cure that by cleaning the tank somehow????
I notice that I have to top up the oil between changes, but that may be typical of the engine???
Also, by very nature of the design, noticable road noise. You get used to it, but I must say that was perhaps the most memorable expereince/difference when I drove my brother in law's Sienna... quiet ride.
So, would I import a 1991 hiace all over again - yes... but having said that, they are notoriously hard to satisfy BC 'safety' regs (headlights), and I've lost track of developments over the past year to know if it is even possible now. Anyone have any word on that?