second note: a v6 is alot more economical that a slant 6 and can make the same power.

i still think a slant 6 is really cool but there is that oil pa pooling thing. move your pickup or have a pan designed. and please use a 6-1 header, itll fit alot better than those big heavy 2 peice. upgrade to aluminum intake and header and head or maybe even have an aluminum block cast and then use slant 6 parts and that will save a ton of weight.

but if you want a 6 cly you may as well get a V6 because its more economical and there are some with a 60 degree bank angle making it skinny and short.

the V6 has the following over the slant 6:

smaller

better economy

more power

more common

lighter

whatever you do you want an engine that has all the accessories to swap over. such as A/C, power steering, all that. you also want it to have been available with what ever transmission you want. i like a manual, i need something that has been paired to a manual or has aftermarket manual parts.

you also need a custom driveshaft and possibly a axle swap from a L series van.

you also need an ECU and wiring skills. this is a downside but youll still have to do some wiring with any engine swap, its a given.

also another thing to consider is the fact that EFI and ignition timing have come a long way. your computer is programmed to tune the air fuel and the ignition timing based off of intake temperature, throttle position, manifold pressure, cylinder head temperature, coolant temperature, oil pressure, oil temperature, engine load, engine speed, vehicle speed, the gear its in, the oxygen level in the exhaust before and after catalytic converter(s) and so many more variables.

your average slant 6 has a vacuum advance distributor that has a curve that isnt accurate, it has a set air/fuel ratio, and it doesnt adjust when hot. and they last about as long as any other engine.