need a bit of help...

damn its a 7 1/4''..i rescued this car from a friends back yard..small 273 2b... i put a edalbrock preformer manifold and 625 demon..new double roller timing chain..tune up and 2 1/4 flowmaster duel exhuast...runs good i believe it has the 905 auto tranny..this is my first street rod...im a vw guy and motorcycle rider/lover...but this dart is growing on me i have the fever as you may say....

my plans are..slap a rear end but still use these small bolt pattern wheels i have....and put the loopiest cam, lifters and push rods i can find preferably keeping stock rockers..suggestions are welcomed...so what should i go look for 8 1/4 or 8 7/5 ..wanna keep small bolt pattern or can i make this 7 1/4 posi...