There's a list of Monark serial #s in the 'NBJ Introduction to classic bicycles book covering 1934-54. The last #s on the list is 1911106, so yours would likely be a 55-7 frame. In late '57, Monark was sold to Huffy, so 58 up are at best a mix of parts, with later models identical to Huffy. FRAME No BICYCLE DATING. HOW OLD IS MY BICYCLE? ‘How old is my bicycle?’ is a question I get asked a lot, nearly as much as: ‘I have a bicycle that looks like one of yours; if I send you pictures please can you identify it for me?’ The answer, in short, is that I do not have time to tell you either. I’m not being callous about this.
Monark Silver King manufactured excellent quality bicycles from the mid 1930’s to the 1960’s and many of those bikes are still around today. Two of their more popular lines were the Flocycle and the Wingbar. Bikes made by this company are either Monark or Silver King but not both. Some models have sold on ebay for as high as $7,000.
In order to identify the exact year of this model, you will need a Monark and/or Silver King catalog. ALUMINUM BICYCLE shown in the photo is listed on ebay for $7600. Unch na 6p3s 2017.
What makes you think it is 'part' Firestone. The chain guard is Monark, no doubt. I can't see the headbadge, but it looks Monark as well.although I could be wrong. The reason I'm interested is that I have Monark/Firestone Special Cruiser.it has a Monark decal on the seat post, and a Firestone Special Cruiser headbadge. The chain guard is like yours, it has the plastic Monark crown insert.
I thought I might be the only one out there with a Monark/Firestone.but you may be the second. Btw, I can't find any info about my bike so if you get some ID leads, I'd appreciate knowing about them. Nice bike btw.not as pretty as my 'Lucy' but really nice.