There are a lot of flathead enthusiasts there in Sweden, so you should also have some local support.
The fellas are correct about perking up a flathead v8, it takes a fair bit of effort and money to get much seat of the pants improvement.
If it's acceleration you want, or high speed, then gearing might be your best spent effort, ratio dependant on which end of the spectrum you're targeting.
The heads would help slightly in cooling, but not enough to compensate for other problems like a clogged block...........which is real common with thesse.
I personally don't think a 97 would give you much over tht 94 that should be on there if stock. The 97 is considered by some to be a bit more "tuneable" which might be the background for the opinions you've heard.
Another area not yet mentioned that will help with getting the max oomph out of that engine would be to make sure the distributor is in top condition, and that the timing is spot on. Helps with cooling as well as general performance too.