What about oxy-acetelyne with a 000 cutting tip?

Plasma cutter?

okay, those both work nicely but they're expensive.

A sawzall with a metal cutting blade or even a reciprocating handsaw aka electric jig with metal cutting blades?

I think no matter how you do your cuts you'll need a grinder for a lot of different things. I was surprised but it is one of the tools I've used the most when restoring my '51- sometimes with cut off wheels, some times with griding wheels, sometimes with wire brushes or cups, etc... it is just a very handy and versitile thing to have around.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi