Replacement Radiator Help and Alum vs OEM style

So, my rad shop has been around more than 30 yrs. Owner told me the only car he ever had to wrestle with was a 396 vega. Essentially, a full cooling system, rad, mech fan, core, thermo should maintain op temp. I had a lean motor that ran hot always. Adjusted the timing and it fixed my prob. 88 dak 400ci. I would start with shroud and make it a wind tunnel, ie block off anything not covered by shroud at this pt