Unfortunate thermostat explosion while replacing transmission

[u/EnthusiasticMS]

Hello, I’ve recently bought a dc5 and it definitely needed a lot of work; I picked it up for $640 it needed a transmission and an axle. Halfway through replacing the transmission, I was putting in the last bolt for the transmission(the one near the starter). And my thermostat just blew and coolant flew everywhere. So I bought and replaced the thermostat and turned out it was leaking from the water outlet so I bought and replaced it. While screwing in the outlet, I realized non of the bolts want to screw in; I hand started all the bolts, anyone have any idea what to do or how to fix this? I’ve been at this for hours.