While the M410 is a very sturdy gearbox and a very FEW were made that will
work on a B20 (and if it was NOT made to work on a B20, it WON'T work on
a B20 unless you get a custom made combination tranny front cover and bellhousing at $$$$$!) there is another issue.

After about 80-100,000 miles there are bearings in the M400/410 tranny that
go bad and start making noise, especially in 2nd and 3rd gear. The tranny
continues to work OK for many more miles but the noise is aggravating and is
certainly NOT a sign that all is well. So unless you specifically NEED an
M410, if I were you I'd stick with the M41, which is also a VERY good box.
(In fact over the years I have explored the possibility of putting one in
my 164 behind the B30 engine and found the reverse swap also requires a
custom made bellhousing at $$$$$!)
--
George Downs Bartlesville, Heart of the USA!