I have a question. Could a 360 LA crankshaft be used in a 273 to stroke it. With a .030 overbore you end up with 300.5 CID. This is just over 0.25" stroke increase. The throw length increase is just over 0.125" so clearance should not be a big issue. This would help in the torque department and compression. Now special pistons with the correct compression height would need to be ordered. Cam selection may need to be looked at. Possibly a 6 pack intake for the looks. A 6 pack running on the primary carb could get excellent fuel economy. For more stealth, a RPM Airgap manifold painted engine color and an Edelbrock AVS2 650 carb would work. You could also use a 340 intake and carb that only the purists would notice as not original.