Budget 318 build

Hello guys I have a few questions and am open to suggestions on an engine im building for my dart. First off its a bone stock bottom end stock heads with a summit k6900 cam and lifters stock iron 340 intake a holley 600cfm 4160 carb and full length headers. The tranny is a stock 904 with a 71/4 rear with 276 gears. I know the rear has got to go!! But the funds arent there yet ! Ok so my questions im gonna go with a double roller timing chain should i get the one that can advance or retard the cam on the gear is this gonna be necessary with this setup? Should i just centerline the cam?What advice would you guys give? Ok next question i have a extra set of 360 heads will the stock 360 valve springs be any better than the stock 318 springs? That is all for know i will post more as they come to me lol