Change oil and see if the problem is still there with the milky oil first. Watch the temp gauge to see if it's running hot. That'd be an indication of a head gasket failure. If your MDC box is totally gone you can toss in an aftermarket temp gauge to see what the engine is doing. Harbor Freight usually has cheap ones on the shelf.
Could be improper winterizing and a cracked block since it's MA. Worst case scenario you'll need a new short or long block. The LTR is just an L31 GM Vortec engine with a 4-bolt main bottom end and a marine camshaft.
If you found a good inboard guy who knows engines you could buy this and have the roller camshaft from your LTR swapped into it.
Should come in way under $7,500.