1970 Duster project in Sweden

I'm sure you already got your answer by now, but as far as new gears for 741 housings, yes, 3.55 or 3.73 are the only ratios I've seen. Now sometimes you can find 3.91s on here or eBay, but those times are few and far between. I found an assembled sure grip carrier with them in the classified recently but it went pretty quick.

Otherwise, looks like you're having a good time with it! If I had the means, I'd find a way to help ship a hotter power plant your way