yikes. get it away from that mechanic, welding a cracked head is silly when you could pretty easily source a head that wasn't cracked. Just put it on a tow truck and bring it to your house and re-configure what you're doing.
So, do you want help spending another 30 grand? Get an e-rod LS3 for 30k with ECU and cats, and find someone to drop that in (there are posts on here describing it) and you'll have a hell of a rig. 430HP and it's CA legal, reliable, etc.
But, my honest advice on what I would do:
20k is a crap ton of money. To me, someone vulnerable to sunk cost fallacy... I would drop a used 3FE that I know runs into it. There are land cruisers with 3FEs all over the place rolling around with 200-300k on the motors and they are just fine. Buying a motor with 200-300k on it, a running one, is not going to cost you that much money, and frankly you could drop one of these into your truck yourself for about $500 in engine, $150 in engine hoist, and $60 worth of tools. This is one of the easiest things I've ever worked on, you've got infinite space to work, they leak oil so none of the bolts are seized, and nothing is that complicated, plus you've got this resource here to explain anything you could imagine and get real time tech support from.
Keep your current motor (seized? like won't spin? what happened) and all the accessories as spares.