I just finished my first ever holiday towing a 4000 lb. 22' 1965
Safari behind my '89 Suburban 3/4 Ton 4x4 with a TBI 350 and I can certainly state; not enough power.
Am now considering stroking to a 383 (and welcome opinions on this) or just look for a new (well, newer) truck but I will miss this one; it came before the A/S.
While some may say "the 4x4 adds weight", well sure, but even if it was a 2WD it would not tow your 27" A/S to anybody's satisfaction.
And a lot of people have warned me off the 454 due to fuel consumption.