Julie,........

Great to have you on the forum, WOW a girl who drives a truck and not afraid to work on the engine. :o) Are you married???? Just kidding.........

Good question, that variable venturi (VV)system s not a good system and has caused many a good mechanic many heartaches, and many have been replaced with a 2100/2150.

Having done this, I can tell you the older 60's models (2100's) are easier than the newer ones (2150's). But be prepared because you are going to have to deal with many of the vacuum tubes and fittings from that VV carb and its swiss cheese manifold (due to all the vacuum ports). Some people (including myself) who have done several of these swaps same themselves some headaches by also swapping out the intake manifold and the distributor as well as the carb. Although this is not necessary.

As far as CFM, for that 351 you ar correct, FORD used both the 1.21 and the 1.23 throughout the later part of the 60's and early 70's on various vehicles including trucks. You should have no trouble finding a good truck carb 2100 from 1968 through 1973 for fairly cheap. Although these days you might end up paying a bit more on E-bay than if you found one at a wrecking yard or swap meet. best bet these days is in the parting section on craigs list or local swap ads, you might be able to score the whole shebang from a bad engine for a paltry amount.

Good luck,

Bill White
White Automotive