Hi Ken
I have to ask, are you sure that you can make an apo lens system using BAK and Flint glass and also are you contemplating a doublet or triplet lens.
Although making your own lens is a noble endeavour , it is a lot of work, as you probably would have realised already but I wonder at the cost and time effectiveness of making your own these days, though the sense of satisfaction and accomplishment on completion would be an enjoyable experience.
As an alternative, this may be an option and of similar specs, give or take a centimetre.
https://www.istar-optical.com/apochromatic.html