If you look in the notes to various other wargames some, like IIRC Panzerblitz and the various manifestations of 3rd reich actually give quantifications of how much aid was received and when and in what types.
As ageneral proposition, Allied aid amounted to about 10% of Russian production in a large number of categories, and the main categories where Allied aid was more than this were TRUCKS and radios, and there where somewhat important contributions of raw materials at times, esp oil.
Most WWII games I have seen the allies actually typically do not send much aid to Russia, and many designers have felt this is how it should be.
In My current game of SEA the Axis targeted russia and we have maxed aid to russia. This is very unusual.
Barbarossa to Berlin imposes the restriction that Lend Lease cards must be played before the Soviets can add many of their mechanized units to their force pools.
Based on my less than expert knowledge, BTB is perhaps the most realistic. While the soviets produced their own tanks in large quantities, the contribution of allied trucks and radios was arguably vital to their effectiveness.
However, our game SEA as we have it does not have OIL rules etc. Last night when we were playing we got into the discussion of OIL. The Euroaxis had left the netherlands neutral, and the Japanese player was introducing the discussion of not attacking the DEI and leaving it neutral and the counterargument was that this game has no oil rules, and so that is why there is no option to leave DEI neutral. The japanese must attack it, or the allies will occupy it and gain the PP. Which is what happened in my last game where I was the allies. I built 2 US CV pre-war and sent a buch of british planes etc to asia, and Britain occupied most of the DEI from early in the game.
What the contribution of Allied aid to the soviets was seems to still be hotly debated. Designers, who presumably did their homework, seem to be consistently coming down on estimating the allied contribution as having been historically lower than many players seem to think.
But in any case, for this game, you are looking for a layer of detail not present, regardless of what side of the issue you are on.
I would add, my WWII era parents Uncles etc were insistent upon the import of allied LL to the soviets. There is an element of propoganda in the belief that the soviets could not have done something without allied help, although if you hold the contrary position, you would say there is an element of revanchism to say otherwise.
I would like to hear the designers view on this.