none of them are easy to fit lol!
some more than others can be made to fit and look good when they're done right. Although I've never done a mk1 dash swap I'm guessing it's very similar to the mk2 that I have done. I've seen corrado and polo dashs fitted in mk1's and they look good.
I was going to fit a mk4 polo dash to Vix's cab, but after she saw some pics I think she's changed her mind....?
Just messure the two and make sure they're not more than an inch different in widths else you'll have either a large gap or a VERY tight fit. The mk1 has flat door cards so they could be made out to fill those gaps fairly easily.
Hope that helps