'70 Duster: Swapped out the original Slant 6/904 for a '72 318/904. The Slant started just fine with the key; the 318 won't even crank - gotta jump the relay terminals to start.

I oughta be able to check continuity at the neutral safety switch with my multimeter. Running thru the gears from park-reverse-neutral-drive, what should I see at the pins?

I'm pretty sure that in P and N the neutral safety should be at ground. I know that if you jump the neutral safety connection on your starter relay to ground, your car will start in any gear.
Hope that helps.

In park or neutral center pin has continuity to ground
In reverse outer pins have continuity to each other... Btw the little metal dot in the center of the plastic button actually grounds through the shifter comb... That is why if you look at the comb there are two metal lines through the plastic comb..

Thanks guys Back to the garage...

move the shifter thru the gears while holding the key in start mode

try starting in N..?

they both had a 3 pin swtch,correct?

could be the shift linkage is slightly out of adjustment,they should all be gone over and adjusted when a R&R has been done.

I have to push up on my truck shifter to get the key to unlock and start in park,i just drop it to N anyways.