Information on the 273

The blocks are identical PN and dimensions, whether the regular 2 bbl or the 4 bbl Hi-Po version. I think that includes the crank and connecting rods. Only the pistons varied. You can buy special Hi-Po pistons today (Egge?), to give higher compression. The 1964-65 heads have bolt angles ~16 deg off vertical (rough guess), which requires special manifolds (factory or old after-market, no new offerings). In 1966, they changed to 45 deg like 318-360 small blocks, so regular intake manifolds will bolt up, though some have taller intake ports. Magnum heads will bolt to all SB blocks, but have vertical bolt holes for their beer-keg intake, though I think you can get aftermarket Magnum heads with 45 deg bolts or regular intakes w/ vertical holes for Magnum heads. So, might bolt any combination of heads and intakes to a 273 block, if the valves will clear the smaller bore of a 273 (some even file the block for clearance). 273 heads are preferred even for a 360 block since their closed-chamber design gives higher compression.

I think all SB blocks, incl Magnums, can use the same head gaskets. But, those will have a too-big hole in a 273. Some people buy NOS 273 gaskets or custom-made ones for the ideal hole. May not be a problem if carbon fills the space over time to get rid of the gap volume, and the gaskets fire-ring will definitely be better protected from flame. You could even make a 273 into a cheap MPFI engine by bolting on intake and beer-keg intake, and add the Magnum flex-plate w/ "toner ring". You cut a hole in the transmission bell-chamber to fit the crank sensor on a bracket (search photos). Could also bolt on a Magnum transmission, which gets overdrive, but must reform the trans tunnel for clearance. Most people have just bolted in an entire Magnum engine and transmission. The Magnum distributor should drop into the block. The engine controller is fairly stand-alone, requiring just a few wires from the car. But, wouldn't give the proper open-loop fuel flow for a 273, so better to use an aftermarket controller or perhaps booger with the Pman signal to fake it for lower fuel flow.