Tom... not quite correct...
It would be fairly expensive to change over to the 4200. Lets say they give you the motor.
Still buying:
Computer
Wire harness lime-swap
Fuel system
Oil pan
Transmission wreckers or use an adapter for your existing trans
All accesories and brackets wreckers
All of the above $1500.
Having to fab up:
Motor mounts
Better electrical system <<<<<< part of the 4200 harness - The '68 harness needs a relay added to power the ignition coils instead of the resistor wire for the old points.
Having to learn:
EFI programing <<<<<<<< not required - Lime-swap does all the hard work for $99
Not saying it would be bad to do. It's good to learn to fab and program something.
A nice running street 250 will put out 250-275 hp <<< Right - NOT unless its turbo-ed or its going to be really lumpy and need to turn 7000 rpm to make that kind of power.
and as much tq. Probably more tq than the 4200. Probably more HP than the 4200 at a lower rpm. NOPE not after a tune goes into the PCM -
this is real data - rear wheel power - 4200 with headers
4200 rear wheel power The 4200 is still a more efficient engine, no doubt.
To do a 275HP 250
you would need:
600 cfm carb or sidedrafts
intake manifold
Lots of head work - big valves, lump ports + a lot of porting
headers
big lumpy cam /lifters
proper damper to turn the rpm needed to make that kind of power
high compression pistons/rings + machine work
and most likely a good set of rods
