Hello:
Could be wrong, but I do not think that the Accurate depiction is more than a rough approximation of Larry's 350 grainer.
Still, just about any properly fitting, .002" over groove diameter bullet, even Lyman's should be fine.
I sent Two Flints photo's of the final Romano Spencer 50 caliber bullet and asked him to please attach them to this.
Larry made a single experimental, two groove, 350 grain Spencer bullet mold and "gave it away to someone who's name he could not recall" after designing and adopting a second design that cast a 315gr to 320gr single groove bullet in straight wheel weights. The final design is for his latest 32" twist rifling. His earlier twist in Douglas cut barrels for the heavier, 350 grain bullet was 36". He told all this to me adding that the 350 will do fine in a 36" twist, but he wanted the slightly shorter bullet for more powder capacity when doing 100 yards. He also indicated that there are unmarked molds that are not his and they are reworked pointed nose blocks with the point welded closed and rebored. Some mistakenly believe his 50 Maynard blocks are for a Spencer, but these cast a 400gr bullet.
Most of Larry's blocks are stamped "LRRCO", and may or may not be cut from Lyman blank blocks.
Regards,
El Supremo/Kevin Tinny