[LS short box]

On my 68 C10 LS swap I used a Afco cross flow radiator. Biggest that would fit. Cross flow puts the inlet and outlet on the passenger side.
The Afco radiator has a "U" shaped channel top and bottom. On the bottom I fabbed a piece of aluminum that fit into the channel. Held it in place with 10-24 bolts. That piece I put three tapped 1/4" holes in using them to fasten the bottom of the radiator to the core support.
On the top I fabbed a "U" shaped cover that fit over the top of the radiator and the used the stock 68 radiator brackets. I did mod the top brackets eliminating the stock shroud mounts.
I'm not a fan of brackets welded to the radiator tanks.
Single 16" Spal fan with no shroud. Never came close to over heating. Fan controlled by LS1 ECM.
Pic of radiator.