A number of people are selling these rod bolt sets at various prices.
See:
http://www.ebay.com/itm/BSA-500-650-Twins-ARP-Connecting-Rod-Bolt-Set-67-1536-1962-72-A10-A50-A65-/121332396810$79 and free shipping?
" New USA Made ARP Forged BSA Unit 500 & 650 Twins Connecting Rod Bolt Set. Looking for replacement rod bolts set but not exactly sure about the quality of new production rod bolts? We understand your concern! Which is exactly why ARP has made these new forged BSA rod bolts and nuts. ARP rod bolts use the stretch method, if you do not have a stretch gauge, you can torque them to 37 ft-lbs, see the installing slip for more details. (ARP lube not included) Fits all BSA A50 & A65 Twins (Royal Star, A50, Lightning, Lightning Rocket, Firebird, etc) from 1962-1972. Will also fit late 650 A10 Pre-Unit Twins (Road Rocket, Spitfire, Super Rocket, Etc) from 1958-1963 with the "large crankshaft journals" only. Please refer to your parts catalog for proper fitment. "
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My good Friends at Rabers parts mart (Ask for Richard) has them for $66.00
See:
https://www.rabers.com/parts.asp?sp=&mcat=&pcat=E&subcat=E2&pg=6 (PM me for a discount promo code)
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I can supply them as well,, $60 plus shipping.