What did post-vocalic r sound like in the UK before it died out?

As far as I understand it most UK dialects became non-rhotic at some point in the 19th century - but was the r sound previously heard in words like park similar to today's American pronunciation, or if not what did it sound like?

Solution 1:

For starters, there are still UK dialects today which are rhotic, especially in the West Country, Scotland, and Northern Island (plus the Republic of Ireland which is not in the UK, but in close contact). Scotland uses a trill, but the others use a very similar R to Americans. This gives us some indication.

The evidence seems to suggest that older varieties of British English and American English sounded more like Irish English. Here's a quick video on how they reconstructed Original Pronunciation aka Shakespearean English which was definitely a rhotic dialect.