An interesting project, Holger, and a tricky one. From the one photo I have, the Arzani-Volpini bodywork curves out quite gracefully, unlike the Ferrari's with those distinct bulges. The nose is probably broader than on the 553. The A-V has quite a large rad. grille. However, it's a good-looking car.
From my one photo, I agree with Tony that a 250F body may be closer than a Squalo's, though the Maseratis had straighter sides. I wondered for a moment if a B-type Connaught shell would be useful. Probably not (for one thing, it doesn't have a fairing behind the driver's head), but you might like to take a look.
The A-Volpini chassis came from the Ruggeri brothers' Milano team but was not one of the modified 4CLT chassis that the team campaigned in its Maserati-Milanos in 1949-50. The Ruggeris designed their own chassis and built two, though just one complete car. It ran in a few races in 1950 as a Milano - probably only one championship race, the Italian GP, driven by Cometti.
Both the Maserati-Milanos and the Milano used 4CLT-based engines modified/built by Mario Speluzzi.
Arzani and Volpini obtained the unraced Ruggeri chassis for their 1955 effort, plus one or more of the Speluzzi engines, enlarging it/them to 2.5 litres. Arzani was apparently an engine-builder himself. The body shape is distinctly mid-50s and is said to have been built by Carrozzeria Colli in Milan.
Sadly, the A-V's only race was the non-championship Pau GP, where its inexperienced driver, Mario Alborghetti, crashed and suffered fatal injuries. The car was repaired and entered in the Italian GP for Luigi Piotti, but it either "failed to appear" or "non-started due to engine problems".
Main sources: A-Z of Formula Racing Cars by David Hodges and Formula One in Camera 1950-59 by Paul Parker. Neither mentions any use in the 1953-54 two-litre period.
The photo in the Parker book (taken at Pau, 1955) shows part of another rare F1 car, the DB Monomill, a small front-drive car with a supercharged 750cc engine. That was a little-used alternative in 1954-60 F1. Apparently the Monomill never ran in a championship GP, but it could be a subject for someone who likes building unusual cars from scratch.