I don't know how long the stroke is, but it was an attempt at big block torque out of a small block(ish) Steve Ossagp or one of the older dudes might know might. Thats what I had in mind for it, on top of doing my other truck related things
I want to get rid of the 16.5's and go to 32's on 16's, which I believe is 285/70R16
Couple things....first to answer the question of stroke, it's 4" which makes it a square bore block also the "M" is intended for the 351 as the 351 is a 400 block with a shortened stroke, the 400 is just a 400, I believe on the emmisions stickers they were labeled 351m/400. Also the 400's had a reputation for pinging due to higher compressions and the decline of availability of leaded fuel in the 70's they tried reducing compression with dished Pistons and backing down the timing curves but they always had the tendency to detonate.