Mystery shudder

I’m not sure I follow the OP but if it starts to shudder when you pull it into gear it could be a bad TC. Check the timing and make sure it doesn’t pull timing at or just off of idle, meaning when you go from park or neutral to gear the timing should not drop. If it does you need to fix that. I’m allergic to the HEI in any form. Had way too many of them that weren’t that good over the years. The last point is just my opinion. I can’t say that that’s an issue or not. I just don’t like them.