1987 G30, Is it worth trying to fix?
 

So 3 years ago I bought an old ambulance on a 1987 Chevy Van G30 Chassis with only 30,000 km on it with the intention of converting it to a mobile home. It ran smoothly but there was lots of white smoke coming out the exhaust and I suspected a damaged head gasket.

I got to work on other parts of the van. Did an Oil change but accidently put a bit too much oil in. I was really lazy and didn't want to do it again so I did some research and what I found online said a little bit over the maximum shouldn't be an issue so I left it. Few days later I was flushing out the coolant system and the engine started making a terrible high pitched screeching noise. I decided this was beyond my skills and it was getting close to winter, so I'd put the project on hold and get a mechanic to look at it in the spring.

I did a really dumb thing. I forgot about the water in the cooling system and let it freeze over the winter. In the spring I decided to change out the oil again and put in the correct amount but when I pulled the drain plug a ton of water came out. I was pretty sure I cracked the engine block, got pissed off about all the money I basically threw away and threw in the towel on the whole project for the last couple years. Now I'm gonna try again but trying to weigh my options.

I'm wondering if its possible that I didn't crack the block and maybe it's because of the damaged head gasket I suspected before that there was water in the oil? Could that also explain the high pitched screeching sound? There wasn't a ton of water in the system, it wasn't even close to full so maybe I got lucky and there was enough room for it to expand without damaging anything? Probably just wishful thinking but does anyone think it'd be worth buying new head gaskets, some oil, and trying to get it working again? Or should I just forget about it...

It seems to expensive to bother with buying another engine and getting it swapped in so my other options are buying a new chassis to put the box on, or looking for another ambulance/van to convert.

Do a leak down test. Gage isn't expensive and will tell you about where your problem is. ...or just pull the engine and see what's going on inside.

A blown head gasket could easily cause water in the oil. If it started screeching while you were doing a coolant flush I'd suspect that you let it cavitate, run dry and killed the water pump.
Are any of the freeze plugs popped out? I don't think the block would be cracked if there wasn't enough pressure to pop a freeze plug.

It's hard to imagine buying a new chassis, and swapping the body over, would be cheaper than swapping in a used or reman motor.