i have been using B-50 but would like to use FF material, i can make my own strings, but wonder if someone kinda specializes in  ff for old bows, and is more experienced at string building than me. This bow has been redone and its a beauty, i just dont want to try FF if its not advisable.

Vintage bows are not FF compatible.

Depends, who you talk to, its such a debatable topic, one person says they are, and the next one says been using them on vintage bows for years, i just dont know what to believe, dont know that its worth taking a chance. Mine is 45@28, i use 16 strands of B-50 and its like a small rope, just wish i knew for sure,like maybe some FF that isnt as severe as others, with good padded loops.

I have 4 Howatts ranging from 1961 to 1974 and all shoot only Dacron.  Unless you redo the tip overlays and build them up I would not advise it. Just my opinion.

Couple words of caution. I experimented with an early Hi Speed that had the typical Howatt underlays but no tip overlays. It shot really nice with a B-50 so I decided to try a D-97 just to see the difference. It made a good shooting bow, a great shooting bow (big difference); however, on about the 8th shot the limb split on each side of the nock at the tip. In this case I can only blame that on the string material. I have been able to repair and re-work that tip with some smooth on and phenolic. It's now back to shooting great but for how long I don't know.

If the bow at least had fiberglass overlays I'd consider the high strength string but I'm sure in your case the Howatt does not.

I make all my strings (mostly D-97 and Rhino)with the loops padded to 18 strands.

Just my opinion but if a bow has no tip overlays or only a thin wood overlay I would not use a high strength string unless the bow really didn't matter to you. I have re-worked the tips on many old bows adding some phenolic overlays. All of these bows have held up well.

Here's one I just finished. It's a Howatt Super Diablo.

Hatrick, Awesome job on the Super Diablo. OM sent.

You could pad the loops to a higher strand count and incorporate B50 into the loops as well, also don't make the string too skinny so it will absorb some more of the energy.  Another idea is to skip the FF and just try some B55 its an improvement.  FF works great on selfbows, you'd think it would work on a glass bow, but I think its more about the construction on the vintage bows than anything.

I would not try F.F. but you can use a 14 strand and get a little more performance from it possibly...I make 14 on all my Howatts,wrap wool to make them more quiet and they seem to give good speed..If the string is twisted correctly you could even get a 12 strand for up to mid 40's bows..I pre stretch all mine so hardly notice any stretching ..
Now I not only worry about what Fast flight can do to the limb tips but you have to also realize that the glue used in the 60's isn't made the same as today's and glue just may loose the bond some what over the years and why take a chance trying a fast flight and  possibly watching a limb loose its bond from the glue/epoxy from the sudden stop in the limbs? I'm no expert in the glue that was used back then but I would just think about it cause that glue /epoxy has 50 years of flexing on them and who knows if it's ever been locked up in a car,put in a garage or attic for a few years unless you are the original owner and took very good care of it over those years.. Me I say pass on the hi performance on such a great bow..

Maybe I will get some B-55 and give that a try, do you use same amount of strands for both  50 and 55. I also have a very nice 67 super kodiak, I would image I would be better to use B-55 for that bow also?

Years ago I saw a Howatt ruined like the one above. This was before the word about FF and older bows got around. Like said before opinions vary. If I did I would use a padded loop string and no less than a 9 gpp arrow maybe a tad more.IMO of course.