IMHO and I am not an engineer, you have 3 choices.
1. Replace the engine with a smaller one, or replace an autobox with a manual or replace the final drive with a longer one.
2. See if someone has done a Diesel conversion and look at that. Diesel engine choices in the US are limited but there is a conversion of a Honda Insight to a 1.2 3cyl TDI somewhere - but that is expensive.
3. And this is one off the wall - back in the day I was a Mini (as in old style Mini not the BMW, er, 'thing') tuner. The bible for this car was David Vizard's Tuning BL's A-Series Engine. This book (>1000 pages) was a masterpiece on how to improve the 1952 OHV, 3 main bearing engine to something that would touch 1.5 litres and make 100hp/litre.
He did include a chapter on building an FE based engine though. I didn't follow it (I was after POWAH) but it did include a lot of stuff about efficient breathing, longer stroke, combustion chamber design and so on.
He took it on a tour of the US too.