I wanted some more scatter terrain for my Back of Beyond and WW2 Chinese wargaming, so I though some appropriate 1920's and 1930's vehicle would fit the bill nicely. 1/56 civilian vehicles designed for 28mm wargaming are hard to come by, so your best bet is to look for diecast cars and trucks that are relatively close in scale (as I did for VBCW). As I only knew of one truck specifically intended to represent a vehicle of that era in China, so conversions of American and British branded vehicles were called for.
First up was the aforementioned ready to use truck, a Matchbox Yesteryear Tsingtao Great Beers of The World 1920 AC Mack (YGB23).For modifications, I only weathered it and added some clear plastic for a windshield. It was nicely detailed for a toy truck and cost me around $15 US with shipping. No scale was listed on the box, but collector sites have given it a nominal scale 1/60, so fairly close to target. When compared to a Warlord Games' 1/56 Type 97 Isuzu truck, they looked reasonable together.Next up were some Lledo Days Gone vehicles that seemed suitable for conversion. The Lledo cars were not as detailed as their Matchbox rival, but at $7-10 US with shipping, they were a good deal (with lots of color variants to choose from).
I have not be able to find a scale guide for the various Lledo vehicles, But I think these models looked reasonable with a Copplestone Chinese figure and against a Warlord Games 1/56 Morris 15cwt Truck.
One additional Lledo vehicle I purchased that did not look good for 28mm wargaming was the DG42 1934 Mack Tank Truck. It should have been similar in size to my Matchbox Mack, but was woefully undersized.
As I think the 1934 Mack variants share parts, I would avoid all of these.
Overall, these came out much better than I thought they would. I've placed some eBay orders for additional Lledo vehicles, so fingers crossed they will look good as well. If you would like to do any conversions yourself, here's the decal designs I made. They are free for personal use, but I don not give permission for them to be sold.
Added 30Aug20: Part 2 of my conversions can be found here.