BR,
The one downside to diluting Linotype by more than 1:1 is getting the tin content below 2%. It's not critical, but 2% is usually the low end of the range given for best mold fill out. Lots of guys use straight wheel weights, which used to have about 0.5% tin, so it's not like you can't use a lower percentage, but it will generally be easier to get sharp corners and consistent weight if you go to 2% or more.
For the .45, I would dilute the Linotype with three parts plain lead, if you have a source, giving you 3% antimony and 1% tin. Then add 1% by weight of most any brand of lead-free plumbing solder (these are mostly 95% tin; just avoid any solder that says it includes zinc, which I've heard exists but have yet to find myself) to bring the tin content of your alloy back up to 2%. If you find some old 50/50 plumbing solder, then use a 2% addition by weight.