15 inch wheels on my Barracuda

I have a stock 69 Barracuda with original steel wheels and stock suspension. I have been running 245/60/14's without any problems. Clearance and driving is OK both front and back cornering and at 80mph. The steel wheels are small bolt pattern with 4 inch lug spread.
Question is the rear wheels a tires: I want to change the rear stock looking steel wheels to 15's and tires keeping the small bolt pattern. How big of a tire size can I go without doing any body or suspension modification? The car is a daily (summertime) driver with a stock factory 340, 4 speed, open rear and stock duel exhaust. Never at the track and no intention to ever modify for high revving performance. I want to "just" give the car a beefier look both in height and width. I'm clueless about the back spacing . Someone has successfully done this before me. OK to send me part numbers from any of the major catalog companies or referrals to any A-body Barracuda parts suppliers. Overall I want to keep the original painted steel look of stock with dog dish covers. Thanks in advance. dg

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You can run a 15" rally rim on the front & back.Usually they are 7" wide and have a 4 1/4 back space. You will have to stick with a 65 series tire because a 70 will rub in the front. I run 235x65x 15R in the back and 215x65x 15R in the front with no problems on a 68 barracuda, summit has the wheels for about $105 a piece, center caps are extra, hope this helps.