318 swap gone wrong?!

Possibilities with fuel in oil and it MUST be fixed. If not and if there's enough fuel, the crankcase can suffer an explosion, blowing open the pan or rocker covers

Some causes:

1...Trying to start the engine for extended periods, you may have gotten a lot of fuel in the cylinders, washed down the rings and cylinders, leaking fuel down in the crankcase

2...I guess you do NOT have a mechanical fuel pump at all? They can leak fuel right into the pan

3...Problems with the carb, mostly flooding, stuck/ dirt in the needles and seats, or "gas logged" floats or leaking brass floats.

Timing. You can check timing on the starter, just don't grind away more than you need to.

You can turn off the fuel pump to prevent further flooding as a temporary measure, turn it on/ off for short periods to try and get it running

Pull plugs and dry, or change plugs

CHANGE THE OIL if the fuel is as bad as you describe.
This i what im thinking, i have cranked it over for days trying to get things right so it made sense as to why it was filled with gas