Should I rebuild the 350 or do an LS swap in my square body, and what does an LS swap really cost?

The case for the LS: better heads (15° valve angle), a roller cam, crank-driven oiling, cross-bolted mains and coil-near-plug ignition. Stock, it makes more power per cubic inch, and it responds better to mods. Speedway rates it the better choice for long-term reliability.

The case for rebuilding the 350: simple, familiar and cheap to repair. Built to the same standard — roller cam, electronic ignition, EFI — a small block can also go 200,000+ miles. Building a 350 to beat a modified LS usually costs a lot more, though.

What the swap costs: it depends on how much you do yourself and whether you reuse the transmission. Our squarebody swap guide lists sourced parts with prices, and the swap cost estimator builds a budget line by line from those lists.

If the truck or car already had a small block, the LS drops in with a handful of swap parts: LS-specific motor mounts (the bolt pattern is different), an oil pan that clears the crossmember, and either your GM transmission with an adapter or an LS-pattern transmission — the bellhousing patterns differ slightly. EFI also needs a harness, a computer and a high-pressure fuel system.

	Small-block Chevy	LS
Valve angle	23° (stock heads)	15°, cathedral or rectangle port
Cam	Flat tappet or roller	Roller only
Oil pump	Distributor-driven, rear pickup	Crank-driven gerotor, front pickup
Ignition	Distributor	Coil-near-plug, no distributor
Bottom end	Many older blocks are two-bolt main	Cross-bolted mains
Dressed weight (Speedway)	about 575 lb	about 430–470 lb (aluminum)