Googe is a wonderfull thing....
1969 3932386 350 4bolt LT1 from:
http://www.nastyz28.com/sbchevy/sblock.php
3956618
3932386
68 - 79 350 & 302 250-300 4 bolt mains
Truck/Hi Perf from:
http://www.thedirtforum.com/castings.htm
WK 1969 350 tur hydro - 255 4 C-10 to 35 from:
http://www.nastyz28.com/gm-chevy-cod...-suffix-10.php
So from three sources... i would say you got a 1969 350, 4 bolt main. Unless it was changed internally