I put this in the wrong place before, I think.
Request for British 3.7" AA guns (turns out they were used in the anti-tank role more often than is thought, especially in Normandy) and US 90mm M1/M2 AA guns, as these were used in the ground role too, as KG Peiper found to his cost in the Ardennes.
I'd definitely go for some 3.7" guns.
According to Ian Hogg the 3.7" was only offically used as AT during the Gazala battle, one battery at Knigsbridge. They certainly used as feild artillery, often in a counter mortar role in the 1944 campaign, since their attatched radar could pick up the bombs. The US did similar with their 90mm. I suspect that most occasions of AT use were accidental.
That said, add my vote for both.
Hogg as a source is very out of date. There's a very long thread here where actual veterans chip in and war dairies consulted:
http://ww2talk.com/index.php?threads/3-7in-aa-gun-not-used-as-at-gun.3970/
with one of the links:
https://rommelsriposte.com/2012/10/09/use-of-the-3-7-aa-gun-in-the-ground-role/
although you'd have to wade through the posts where people confuse the references to ground-firing artillery role with anti-tank direct fire. It is clear that there was a systematic training programme set up for HAA regiments to operate in the anti-tank role when required, with APHE being issued from 1941.
Interestingly, I recently saw a photo of a Stuart tank pulling one of the last surviving 3.7" AA gun from the Knighsbridge box.
Mark
Votes added!