thats real close to what im putting together now sept with a lil bigger hydraulic roller in a factory roller cam block, same intake n heads with alotta home porting 750dp carb, 3000 stall going in a 73 duster, got about 650 buck in it all so far....
I felt bad using a flat tappet in my ('87) block, but it had always been a hyd flat tappet (stock 2bbl truck, later a .430/.450" Purple hydraulic), and all the roller cams I had then were in use or obligated to other builds. You're gonna love that Duster, I did a '92 Jeep 5.2L Magnum for my '68 Dart and used a 218/224*@.050" Comp roller (custom back then, now a XR270HR-10) and ran as low as 8.20s at 86mph in the 1/8mi. I had a tight converter which was killing my 60ft. times, so depending on your cam, you may need a tight 9.5 or 10" converter, mine was 11"....
