Im going to be swapping a edelbrock performer 600 cfm carb, edelbrock rpm airgap intake and some hooker headers and a true dual exhaust onto my 1985 W150 prospector. Currently it is a 318 2 barrel and my two questions are; the kickdown linkages are different(correct?), and what kind of gains could I expect from the swap?

Yes kickdown is a bit different. As for gains, your parts will help, however your main bottleneck is stock heads flow so little and a tiny stock cam. I wouldn't run the Air Gap intake with stock port 318 heads, the runners of the air gap are going to be larger than the intake ports in your heads that all they're going to do is cost you some throttle response. Really a small port 4bbl intake would have performed a bit better in the bottom end in your basically stock application.

When converting your 2bbl 318 to a 4bbl you will need to convert the linkage. The stock linkage
can be adjusted(all the way out) to get this to work but it will become very flimsy..

Get a 4 bbl linkage off of a 4 barrel Diplomat,
or similar 4 bbl 318/360 car... 1978-1980's

AS for horsepower... the 4 barrel upgrade won't really buy you much, maybe 5HP.. You'll notice the kick mostly when you floor it going 30 mph.
and when you are at highway speed and floor it to pass somebody...

The headers will add the most bang for the buck.
There was a good writeup recently in either mopar muscle or muscle car review (I'm sorry I don't remember which) about exhaust upgrades on a small block mopar.

The exhaust should give you a 10%-15% boost in horsepower.. I believe you will get a little more with the TTi step headers vs. hookers.

To really get a jump, put on some 360 heads
(1.88 intake 1.6 exhaust) and bump the cam.

Best of luck...

Thanks for the responses. The only reason I was going to put on the air gap is because I was originally going to put on the stock 340 intake from my cuda and a thermoquad but my car is still at the body shop waiting for paint so it will be a while. Im not looking to go racing with the truck or anything, (just make it have a good amount of more power because it is very slow right now) so I will stick with the hookers instead of spending the money for TTI's since I only drive this in the winter and bad weather.

port mismatch not that big a deal breaker IMHO

the intake is gonna need a taller bracket for the throttle and kick down rod

on my LD4B/LD340 intake a stock truck q-jet 4-v bracket and linkage worked

I went to full manual VB on the 85 truck going to a 440 to loose the TPV linkage

IMO.a stock 4-v intake and a mopar q-jet would be the best,truck came with it,it will look stock and it all fits and work correctly

the LD intakes are the next best fit when it come to working the linkage

rpm air gap is a tall intake and will need the bracket and linkage

and hope it works correctly

if it dont you will toast the tranz in the long run by it not being adjusted correctly

DAMHIK

a Bouchillon kit would be the next step over the stock linkage

or use a full manual forward shift low band apply valvebody and then it no need for the linkage

good luck

I also have an LD340 but that is for my cuda also, so maybe I'll just have to wait to take the stock 340 intake off and just do the exhaust for now.