according to Way's Packet Directory the Van Dorn was a former towboat named Junius Beebee. it lists the dimensions as 182' x 28.3 x 10.7 but doesn't list a tonnage...however th General Lyon with similar dimesions (182.1 x 35.8 x 7.5) is listed as 390 tons.

the Van Dorn being a former towboat with a fairly deep draft was probably a little heavier than that so around 450 tons is probably close.

Way's doesn't list dimensions or weight for Jeff Thompson but all those boats were probably in the 300 to 500 range.