Lost a Timing Chain while starting up

I'm a new Member , I spent all day yesterday determining
what was up with my 450 SL 1980 merc,

I've had it for 20 years and I've replaced trans radi fuel pump etc.

Just put a new soft top car is cherry. I washed it Sunday,
put it back into my garage and an hour later I went to start it and

lord have mercy Great rattle bag lifter topend sound.
I stopped cause it wouldn't turn over, i thought it wasn't getting
fuel from the fuel pump so I banged the rear where it is and started it again , this time it started and bang it started,

thinking it would calm down I let it idle for about thirty seconds untill I realized this is a sound I 'm not familiar with.

Looked under hood next to power steering pully there was a crack in my valve cover.

Doh how could a timing chain go?

I got a estamite from my mechanic for valve job and chain and guides head gasket the works $2300 total for everything?

I'm not sure if I need all the valves done yet but I figure it's probably what's need.
Is that a good price? since I wasnt driving it could it be cheaper?

thanks for any input , nice to be a member.
Maybe being a member I won't have these things happen again to me.