Thinking of re-powering my SBC V8 car, In the planning stages need ideas for budgeting Options

[Rider914]

I have a '72 that has been V8 converted for the last 30 years.
The old SBC is tired and leaky and I would love to switch to an LS for more power and fuel injection. Definitely LS3 or maybe LS7 if they have fixed the valve problems. Minimum of 600 hp, more is better. It has massive tires so traction isn't a problem.
I could be talked into turbos...

Must ditch the 901 tail-shifter. The Boxter S sounds promising. I dream of a sequential but $$.

Car is a garage queen that will get some track but 98% street and shows. 200 miles a year.

What crate engine should I look at? ECU/Spark?

Just trying to get the budget numbers. Would like to shoot for $20k or so.

Thanks