You must have some bastardized joist to have a top chord of two angles
2x2x3/8". I find an old Ceco catalog from the mid 60s showing a number 8
top chord section being comprised of 2Ls-2x2x3/16. On the 18H8 joist the
bottom chord is 2 rounds 15/16" dia. and the interior web members are one
round 5/8" dia. with the end diagonal being one round 3/4" dia. The panel
points are 20 inches apart. The 3/8" thickness of the top chord section is
kind of out of line with the joists of this era.
I would be mighty carefull as they could just as easily be of the old "S"
series and the load capacity would certainly be reduced.