If you wanna go with the normal wave of people but the Sixes are better on fuel if you get it just right. 1bbl IS a gutless wonder...my 70 Dart had a 225 1bbl. I swapped out to a 2bbl Cast Iron intake and put a 2bbl 500cfm...ran better...not great. I swapped out the cast iron and found a 4bbl Offy Aluminum and ran a 4bbl 390cfm. Ran better and was content...Then I swapped out the atrocious exhaust manifold. Put in the 6-to-1 MP header...Ran better...not great...the #4 pipe had to be crushed to fit the steering pump. Eventually switched out to the Clifford Tri-Y Dual headers. Breathed ALOT better. Sent out a spare cylinder head and had it rebuilt. 5 angle valve job, new large valves (1.61/1.34 IIRC), mild Porting...I wanted to put 5/16" vave stems from a Ford but the guy said it was wasted money. Bolted it on....difference was night and day. Had to get rid of the 390cfm Holley....tossed it and went with a 500cfm Edelbrock.....I broke the rear end. 3 of the 4 spyder gears went bye bye. Don't underestimate the power of a slant. I was taking out small blocks with mine and I was the only muscle car on the road in my area during the gas crunch of 2002/2003. Went back and forth from LA to Vegas on numerous occasions.

If you are worried about the linkage, switch to a Lokar for the kickdown or go one and done with a Bouchillion Kit that you can use from a Slant to an RB and set that throttle/kickdown any way you see fit.

While you are up to changing things (If you keep the Slant) put in a remote oil filter. I hated bathing my suspension in oil at every oil change

More pics on the link in my signature but..