Rebuild my SBC or new engine options

[Jaconense777]

.Hello guys, I have my S30 and it already has a 350 in it, I found out some milky ( hard to see) stuff on the radiator cap so I assume it’s a blown head gasket, it has a custom driveshaft, turbo transmission, it has an Edelbrock  6073 aluminum heads conversion kit and performer manifold, 1406 carburetor , hooker headers, ceramic coated twin Anasa exhaust system... my concern here is that I might be in the need to rebuild the whole engine, and hope the heads aren’t cracked as aluminum heads tent to crack, and if that’s the case I am wondering if it’s cheaper rebuilding the current engine or buying a new one, and if the heads are reusable use them on the new or rebuild engine, or should I go a different route, with a different swap, I was thinking about a RB25, I’ve seen some around $2500 with Transmission online (but I’ve heard that parts are a pain to get them), if so do I need special modifications? In the conversion to a V8 350 I noticed  it was spent over $3300, i don’t want to complicate things and make it easier  with your advice and suggestions, I don’t want to get ripped off by a mechanic so I’ve been doing some research and what better place that with experienced Z drivers. Thanks for your support.

( I already spent many months in bed, about 8 months for cancer then 6 months in a hospital  so now that I can walk want to fly on my Z lol) 

[Jaconense777]

Forgot to mention is a SBC 5.7 engine.

[caperix]

Does the car have any driveability issues, or over heat?  A compression & leak down test or a coolant co2 test will give you a better idea what is going on with the engine.  Oil can get in to the coolant at the intake gaskets as well.  Rebuilding the engine in it will be cheaper than any swap, so unless you have the time & money to redo the wiring, fuel system, driveshaft & exhaust I would keep the sbc.