Why not just aim for a used for your "Big Block" conversion?
Would save you quite a few bucks for parts 
I just stubled on this, which doesn´t look bad to me:
https://www.ebay.com/itm/WILESCO-STEAM-TRACTOR-APPEARS-NEW-AND-UNUSED-MADE-IN-W-GERMANY-VINTAGE-TOY/133698304020
Furthermore has the advantage of being old enough, to have a "real" steamvalve on there.
That solder job just above the throttle looks very suspect to me....doesn't look factory done.
Sharp Eyes Bruce!...it does look resoldered...He is advertised as "appears New" but I can tell from slight discoloration on bottom of fire tray she Has been fired. If no one bids I do think it is still a pretty decent value. The last 5 min of auction will tell the story.