I presume you're talking about the Radisich allcomer?

In 1964 Radisich raced a Mk2 Zephyr with an ex-Sprague engine. For the following season he dropped the engine into a Humber 80 - from memory the car was a Series I but I don't know whether it had been raced by an earlier owner with its original engine. The Zepyhr of course passed to Rod Coppins who popped a Corvette engine into it

For 1966 Frank replaced the engine with one from a crashed Jaguar XK150

I don't know anything about the Humber 80's construction methods, but do know the six-cylinder engines went a long way back into the passenger compartment!