Just installed a new oil pan on my early 327 and what I found was that front seal thickness is dictated by the pan, not the timing chain cover. 55-74 sbc's used the thin seal (felpro 34509t) and 75-85 used the thick front seal (34510t). If you're not sure what you've got, lay a straight edge across the front oil pan rails and measure down to the pan seal lip. 2 1/4" uses a thin seal and 2 3/8 uses a thick seal. 86 & later use a thick front seal but require a 1pc rear main seal. FWIW, found the least expensive 34510t @ O'Rielly's; about $22 + tax.
Hope this helps.
70 Nova, 327, AFR, TRW, Perf RPM, Holley dp, Comp xs268s, DIY HEI & cowl air, headers, 4 spd, PowerTrax