273 to Slant Six Conversion?

I haven't looked at the Offy linkage bracket setup, but your V8 car will already have a cable-type accelerator setup. You may be able to adapt the existing V8 kickdown linkage, or see this thread for kickdown options.

Good news for slant-6 buildups is that you don't need to gamble with Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example Dutra Duals and header options discussed in this thread and this one, Erson custom cams, HEI ignition upgrade, Mike Jeffreys windage trays, Hurricane intakes, other exotic intakes. Hi-perf engine buildup here, high-perf parts and build info here.