The 3B is a very reliable and workhorse kinda engine. Very similar to the 3F you had in your RKR, minus the fuel it runs on. I've sat in a 60 series LC, owned by Nuic, with humango maniac tyres drag along in the city just fine. Sorry, don't have specifics concerning economy. I think however, you would miss some torque the old 3F was able to deliver. BUT!!! I hear you can add a turbo if you're bored, and effectively make your 3B into a 13B-T!! And that is a pyscho diesel engine. Coil sprung?