The Redline Twin DCOE Manifold was designed by Warnerford Australia, originally 42mm in - 38ish out with couterbores for the alignment with B18 Heads &  sold them with 42mm DCOE's. The design is to fit on 120 series & look good, but they are way too short.

When Warnerford went out of buisness, the next company came up with two manifolds  #1 45mm in - 40 out, #2 40mm in 38ish out. When Redline bought that company, they choose #2 and slapped Redline on it.

I bought a new #1 style in 1986. I went looking for a spare in the early 1990's & found that Redline only made #2 & bought that for a spare. So I seriously doubt that manifold in that K901 kit would have 45mm holes in them. So, Ask them for a picture of the inlet & outlet sides with a ruler laying across the holes.

I wouldn't use the twin heim joint arrangement either, use one on the front & use the original arangement at the rear & use a Weber style interconnecting link, OR, buy the cable style kit. The folded sheetmetal linkage levers are junk too, Thick CNC ones have been around for 30 years now.

Flow wise, with the #1 style manifold, it's adequate for modest heads with a modest cam & the B20E exhaust manifold. To get one to breath on a performance motor takes a lot of work. I start by cutting the flanges off the injection manifold & weld them on to give some chance of making the thing flow.

Finally: https://www.carburetion.com/Products/ProductDetails.aspx?part=K901 says "Applications: 68 - 72 B18 B20 manifold upgrade" That tells you it has B18A/B B20A/B sized holes

MISAB.SE makes one that looks like it is as long as the Volvo Factory, but when fitting DCOEs to a 140, the extra length makes them work the best.