I did a lot of research on this and you can find the conclusions
here.
Most of these are long blocks but it certainly gives you an idea of possible starting points to move forward in cost to a plug an play.
With that said, first pick your fuel delivery preference. Fuel injection or carbs. Both will work and have their pros and cons. But if you want performance a modern FI engine management system gives you a lot of control that you don't get with carbs.
Stick with reasonable P/C size increases. Going to a 105mm P/C gets you displacement but unless you are going to have LN nickies there will always be a heat concern.
A 2.3 with the right parts can make a very good running engine. Unless the engine you get is built by someone with talent like Raby, it is difficult for most builders to push it beyond the 2.3 with out issues.
So even at the 2056 level a build with a good cam and big alve heads can make a really fun package for a reasonable price. At 2.3 it starts top get expensive but very fun.
Without details it is hard to tell if the $8k is a good deal. But you can certainly do it for less.