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I've noticed a lot of people (myself included) ask about the restrictiveness of the engine family system. I understand why you've made it the way it is. So here is my suggestion:
In the tycoon mode, have the ability to create new engine families based on existing ones. So for example if you have a SOHC engine, you can start a new family of DOHC engines that are otherwise identical to the SOHC engine and save development costs over designing a new engine from scratch.
This system could also be used for changing block and head material and changing V8s from crossplane to flatplane. Another thing I would like to see is if you could adapt one engine type into another, for example the Triumph V8 was essentially 2 of their existing I4s joined to a common crankshaft.

That system you are proposing is not needed because of the component familiarity concept in place. The more you produce for example alloy heads, that carries over to any new engine family you make and cuts down engineering time. We think that will serve the purpose you would want to see.

What about pushrods? Will experience in pushrods help with producing modern pushrods, or the bonuses only stay for normal pushrods?

The familiarity will help you keep engineering times down, so you will be able to use higher quality, which indeed helps revving pushrod engines higher.