Rum & Thumper Question

[SAS777]

Another rookie rum question.

I recently purchased a thumper from Mile High for my 13 gal. boiler. I used it once on a batch of corn, and it came out great.
I also purchased an excellent condition used 5 gal whiskey barrel with stand from Mile High. I want to fill the used whiskey barrel with rum. With needing to fill it with 60% - 62%, I'm afraid of how much blackstrap I will need to purchase.

My question is:
*To try and keep cost down, can I cheat by making 5 gal of dark brown sugar wash and 5 gal of blackstrap wash, mix the 2 together in my 13 gal boiler,
but hold back ~1.5 gal of the blackstrap wash that I will put into the thumper?

* By putting the blackstrap wash into my thumper, will I get close to the same flavor as if I used all black strap?